John Pearse (the string-maker & guitarist) makes a similar item that basically hangs the guitar on the edge of a shelf or similar horizontal edge, without needing to clamp it. I suspect you could use Pearse's cantilevered gadget on tables. I'm going to John's website to see if it'd work.

Be right back.

It's called the "D'Angle," and it might or might not work on a table. It looks like it requires the instrument to rest against a vertical surface to be stable. You can see them at:

http://www.jpstrings.com/braccess.htm

I'd ask John, if 'twere me. In fact, I think I may just do that. [Possibly more on this later.]

Bob Clayton