Hey Steve,
Some people have tried flexing spherical mirrors to mimic a parabolic figure. I have seen articles on this in Sky and Telescope (USA). Do a search (I will do one as well) and see if you can come up with something similar. They use epoxy of something to mount a long bolt onto the back of the mirror (in the middle) and then thread this through a metal back with a central hole bored into it. This piece probably needs to be strong so when you start to tighten the wingnut, the mirror will flex instead of the metal back.
Hope that was helpful.
Darren
http://forum.ourdarkskies.com/lofive...php/t4388.html