I came across this article for a string tripod - both ultralight and multi-use.

You can use anything from a guyline to dental floss or braided fishing line.

I'd call it a monopod before a tripod, but that's just my rambling.
The best feature of this is, unlike other tripods/monopods, it's compatible with every quick release plate ever made!

The tripod aspect of using a single string would be that your own legs or other bodyparts also act as pod legs. Leaning against a tree adds more support.

Drill a hole in a detachable base plate for the string so that it can still be used in an actual tripod or monopod.

I have a walking stick with a screw off top that will take a camera. Adding a string guyline to that set-up would add additional stability.

Many hardware stores have 1/4" nylon threaded thumbscrews. Drill a hole in the thumb part.

http://www.backpackinglight.com/cgi-bin/backpackinglight/xdpy/forum_thread/13758/index.html?skip_to_post=102387#102387

Yeah, it's an old trick we used to do. It works best if you pull up on the string while locking your arms into your body while cradling the camera from underneath. But with long lenses it's only slightly better that freehand, your pulse is still coursing through your body. Now if you shoot between heartbeats...