I am sorry no one has come forward with some help for your original quilt idea. I am not certain I have ever seen or heard of a quilt make with the whole garment. I have seen quilts made from pieces cut from children's clothing, and that would not be difficult to do. But your idea is something that would seem to be similar to doing applique. That is the only way I could picture using whole garments.
Perhaps you could lay them out in a collage sort of fashion and maybe take photos of the effect you like. Then you could applique them on your background fabric (even a sheet) This is where the photos would come in handy, because moving pieces around could distort the design you had in mind.
It is a very novel idea and I am sure some help will come along after we are past the week-end. But I wanted to encourage you not to give up because the gals here are great about being helpful.
Hang on to your idea. It sounds great. Keep us posted as you figure out how to do this and be sure to take photos as you go.
June in Cincinnati.
P.S. I found this site that was interesting...http://mijafiberart.com/ These are "radiant illusions from vintage clothing." They are a bit far out, but at least you can see what someone else was trying to accomplish.