Hm. The optical theremin makes me think of another approach: using IR LEDs of different frequencies (assuming I can get those...) and appropriate IR receivers mounted along the palm, and using proxmity to the IR receiver (ie, intensity of light received) to determine position of the fingertip switches. Or maybe some kind of gesture-based thing. For the thumb switches I could use something similar to the reset circuit in Mitch Altman's Trippy RGB Waves (http://www.tvbgone.com/cfe_trippyRGB_instructions.php) kit -- cover up the LEDs to interrupt the light, since those switches are meant to be binary. Though if I can get enough positions out of the fingers, I might not actually need the switches. My hands aren't super-flexible, though -- curling one finger enough tends to make all the other ones curl too -- so the design considerations are going to be interesting.

I do hope you can make it to HAR!