zvex effects!

so the company zvex makes a line of effects called 'probes'. the amount of effect applied is controlled by the distance your foot (or hand or whatever) is from the copper plate on it.
not exactly a theremin, but somewhat related. they have videos on their site of them being used. pretty cool in my book.

http://www.zvex.com/effects.html

I checked out the "Wah" video - those guys know they are doing with putting out a demo video! Very direct and very clear, with a touch of attitude...