OK, so make a groove in the bottom (just wide enough to hold the glass) and use something like a bathroom mirror retainer at the top to hold it in from the inside with screws, or you could put in a wooden frame behind the glass that's screwed into the sides--use your imagination! I don't know if you really need much support on the sides, since 1/4" Lexan is pretty rigid.
I would definitlely use Lexan instead of glass if you're actually planning on hitting the machine at some point...
Myself, I'm planning to treat my machine a little better, since I've put a lot of time and money into it! For most people playing at home, I don't think it has to be as indestructible as a machine that's made to be left anattended at an all-night laundromat.
Maybe someone else has a better idea, just a few suggestions from me...