Don Baccus , Dec 30, 1998; 11:53 p.m.
I have absolutely no suggestions, but this is such an unusual yet crucial question (to those confined to wheelchairs) that I would encourage you to find an off-the-shelf solution if at all possible, and to then write an article for the main photo.net information section so that others so confined could learn from your explorations and experience.
I recall seeing one magazine article on this general problem of how to support a camera from a wheelchair many years ago, but don't know where. Outdoor Photographer? Modern/Popular photography? Unfortunately, I don't even clearly remember HOW long ago I saw it.