You know... I've been toying with the idea of designing a clamp that allows 1) positive locking of rear wheel (can't shift out of the drops) and 2) uses a threaded fastener to adjust the location of the wheel in the drops. It would actually have to be a pair of clamps that sit on both sides - both drops. I envision something that would allow for fine tuning chain tension and trueness of the wheel (...how parallel it is to the centerline of the bicycle).

Ever come across something like that? I've seen 'locks' on front wheels but not the adjusting functionality.