Is there such a beast as a vertical grip (kind of like the rail mounted ones for weapons) that screws into a tripod mount? I.e., something at most ten inches long (not as long as a monopod), not for holding your camera off the ground but with your weak hand. I would really like to get one.

I was checking out the cameras at Best Buy and noticed that they had such a thing attached to the display cameras (though it was a security device). It felt pretty comfortable and very stable.