Olympic lifters squat with elevated heels all the time (due to their special lifting shoes) and I observed they usually have solid quad development. In any case youre still working your posterior chain, just transferring a little more effort to the quads.
Grab between your legs see if you still have a pair, then try to man up!!
You will note that the great TC himself elevates his heels for front squats.
(Full res photo at http://www.T-Nation.com/readArticle.do?id=1504100.)