What about something like this: one piece on each surface of the inside, and they're both a quarter arc in shape and the top part has an end with a knob that fits inside the lower part (which has a slot) and slides in it. I can't think of what that might be called, but I know I've seen it. Would solve lots of issues, including being nice an tidy.......na, wouldn't be stable, though. That's only a sort of guide to support a hinge. Hmm.