This page is in response to a question about who may be using a monopod set-up with small or mini-tripod support. This is only an explaination of my set up and how I use it.
There are obviously many other ways to do this. This is only my example.(Please consider this my disclaimer)
This set-up is inspired by a write up regarding shooting panos in a gondola in Venice, Italy found at the VRWay.com on-line magazine. It describes a set-up up used by VR expert Hans Nyberg.
Here's a direct link to this write up:

http://tinyurl.com/2t2hlw

-----This begins my disclosure-------

Here are the catalog numbers of the items I use:
From Bogen-
-3007 mini-tripod kit

-3049LS Metz Adapter screw

-3154 dual female 3/8" adapter

-300N Indexed Rotator

-682 (3231) Monopod (with Detachable Legs)


(Which I suppose is basically a regular monopod that includes)-

-Bogen #678 Universal Folding Base for Bogen Monopods -

The 678 (which can be purchased separately) comes with:
-Three legs,
-A metal sleeve that slides onto (and attaches via 3 small set screws) the end of the monopod's smallest and last extention,
-A large custom metal screw(the bushing as Milko describes it and I will too for the rest of this tutorial) that holds the legs in two positions.
-One position out, allowing the monopod to actually become a tripod with a very tall center column
-the other position in with the legs folded inside the monopod's last extention.
-A removable pin (not pictured) holds the legs into the bushing and is threaded into the center of this piece, revealed by removing the next piece
-A small rubber foot in the center of the bushing that serves as the foot of the tripod.

After removing the rubber foot, I unscrewed the small pin that holds the legs in place, thus allowing the legs to be removed from the bushing.
Then I had the lower portion of the bushing ground flat(see "Notes" below for description of this process).
After this process, I had a 3/8" hole drilled and threaded in the place of the original hole that held the small leg-retaining pin. The result is pictured here:


This is where I mount the lens ring or nodal point bracket with either the Bogen Metz screw or the extra brass 3/8" screw that came with the Bogen 625(see below "Alternate set-up" description for explaination of the the use of the 625).

The entire set up from the top down-
-lens ring
-Custom bushing from the Bogen 678
-682 Monopod inverted (upside down)
-3154 3/8 adapter where the camera would normally be
-300N rotator.
-3007 mini tripod

With this set up, I can be very nimble in crowded places:

http://tinyurl.com/yvmwqn

In this example, you can see a very similar set up in front of Jook Leung

The tripod is small and sets up instantly and can be used in places where regular tripod use is impossible(or at least not likely to be successful:

http://tinyurl.com/yrvrfw

I can also push the tripod into my gut and get a little higher:

http://tinyurl.com/2ekn39

Or I can use the set up horizontally over the edge of a bridge or similar place:

http://tinyurl.com/2a5tk5

I really enjoy the size of the set up and often use it to hike and shoot without holding up the family:

Why do I use the monopod inverted? When used in intended orientation, the monopod gets bigger as it gets higher, thus making it top-heavy. Also, the customized bushing only has a small surface area to fit onto whatever you're attaching it to(mini tripod or 625 QR plate system). Inverted, there is much more surface area to work with(to attach the 3154 adapter to). And it gets smaller as it goes up.

 

"Alternate Set-UP"

The set up can be mounted on top of another tripod, thus reaching higher by using the:

Bogen 625(3296)Quick Release Plate/Base instead of the 3007 mini tripod

In ths instance, the QR plate is attached to the bottom of the 300N rotator and the base to the 625 QR system is mounted to the top of a tripod for easy on/off from the top of the tripod.

As an alternate to the lens ring-
I will use the Nodal Ninja 3 bracket. This bracket has a removable rotator. After removing the NN3 rotator, a small brass piece can be removed revealing a 3/8" threaded hole. The brass screw included with the Bogen 625 fits nicely down through the NN3 into the customized bushing:

What's great about this set up is the use of the Nikon 10.5mm lens. Yes, I can only create barrel projections like this(with the Canon 1.6 crop sensors). But when this set up is used on top of another tripod with the 625 Quick Release plate system, one can shoot the desired number of shots around, then quickly remove the monopod, lower the monopod set up, adjust the NN3 to point the camera up, replace the monopod and take the zenith shot. Repeat for the nadir and one can produce a pano similar to this:

http://tinyurl.com/37qdrr

In this example, you can see a shadow of the entire set up

Regarding the use of the NN3, I only utilize this when the set up is used with the 625 QR plate system mounted on another tripod. I've found when the NN3 is used, the whole thing it too top-heavy to be used with the 3007 mini tripod.

 

Notes:
-The main reason for this set up instead of just hand holding is the ability to bracket(or to use extremely slow shutter speeds) without worrying about alignment.
-Another reason for this set up is repeatability and ease of stitching(there is no guessing on rotation spacing-a basic template is re-applied to each pano during production).
-I never step away from this set up as the legs of the mini-tripod only have a radius of about 10 inches(25 centimeters).
-Shooting with the 8mm requires an extra "down-shot" to get nadir coverage. This is easily achieved by holding the system horizontally over the nadir.
-A cable-less remote and camera with built-in receiver(such as the Canon Rebels-350D/400D/450D) helps greatly. A cable release does work though.
-The small leg-retaining pin is basically useless(for any application here) after the 3/8" hole is tapped through the bushing.
-This is also the case with the rubber foot.
-The legs included with 678 can still be used with the customized metal bushing.
-I wouldn't recommend a large pro-camera with built-in vertical grip like the Canon 1D(s) or Nikon D2/3 as this too will make the set-up much too top-heavy.
-With the Bogen 3007 and 300N and another unmentioned piece, the Bogen 3358(an adapter that allows the mounting onto a 3/8" threaded post and providing a 1/4" post):



You've got all the fixings for a nifty little table-top pano-head:



If your lens ring has a 3/8 mounting hole, you don't need the Bogen 3358 as the 3007 extention has a 3/8" threaded post

Here's and example table top pano:

http://tinyurl.com/2tp8lz

-A small quick release system attached to the bushing for easy on/off of the lens ring would be highly beneficial. Currently, the best way to separate the ring from the monopod is to unscrew the bushing from the sleeve that's attached to the monopod, leaving the bushing attached to the lens ring. I haven't found a small enough QR system with enough grip to give me confidence to mount the ring to the custom bushing. The QR systems that I'm familiar with are either too heavy and intrude into the FOV or just inadequate for security.

Regarding the grinding down of the bushing:
It is made of aluminum and is easily ground down with a bench mounted belt sander. The bushing was mounted in place, (attached to the sleeve which was attached to the monopod) thus allowing the holding of the entire monopod during grinding. Also - there is a rubber o-ring between the bushing and the sleeve to prevent over tightening during regular use of the two pieces(this part isn't mentioned above but can be seen in the first and last close up images of the customized bushing). This was temporarily removed before ginding to prevent friction heat from melting it. Grinding was done in steps to prevent the two metal pieces from being fused together. A little grinding, then wet the pieces, dry, grind again, wet, etc...

Regarding the lens ring used for this set up:
Currently(as of the writing of this tutorial), I own the Sigma 8mm/f:4 lens. I don't have a proper lens ring for this lens. But, I do have a Canon 70-200mm/2.8 IS lens that comes with a tripod mount lens ring. This lens ring is not appropriate for this lens as it is too big to tighten down on the Sigma 8mm. This lens ring has a small amount of tightening adjustment made specifically for the Canon 70-200mm IS lens. To make the Sigma accept this ring, I wrapped it with painter's border tape until it was big enough to allow the Canon ring to tighten down securely around the lens. This tape is made to be removed from surfaces after use so hopefully it won't leave much of a residue. And it is considerably cheaper than using real photo gaffer's tape. The tape provides a second function of holding the focus ring in place. I usually have no use for focusing when shooting panos with the Sigma 8mm as I have the aperture set at f:8. Also, wrapping the tape as one long piece, the size of the lens grows evenly so the ring keeps the lens in the center. This Canon ring has a 1/4" threaded hole instead of a 3/8" hole. So for this set up I use the Bogen Metz screw to hold it to the metal bushing from below.

This Canon ring has a large foot that protrudes into the lens' field of view. I also had this piece ground down as much as possible without compromising the 1/4" mounting screw hole. It is made of aluminum and is extremely shiny. It still is visible in the lens' FOV. To help alleviate its presence in the image, I've covered this piece with black gaffer's tape.