If you were feeling handy, you could try drilling a hole in the center of the glass at the bottom of the cage and then putting a raised second floor (plastic/pvc/abc sitting on a 1/2" riser) in the bottom that angles into that hole
You'd need to make sure of a few things first though.
1) The glass can't be tempered glass or safety glass
2) You need special bits for glass (buy them at a hardware store)
3) You need to go slowly and keep drilling slightly larger & larger holes to avoid breaking the glass.
I'm sure there are good tutorials on the internet on how to drill glass.
although a few thoughts on drilling glass since i do it all the time for aquariums..correct about tempered glass--it cannot be drilled. usually only the bottom pane is tempered so all the sides can be drilled. check first, though. second, diamond tipped drill bits are not easy to come by--large enough ones to fit a bulkhead are not in any of my local hardware stores. find them online: http://www.bulkreefsupply.com/store...its/45-mm-diamond-coated-glass-drill-bit.html. last, look up tutorials on youtube, you DO NOT want to drill a small hole and progressively make it bigger (plus this would require multiple expensive bits), you just want to drill one hole. start slow and put no more pressure than the natural weight of the drill..do it in the bathtub if possible so the water can wash away the glass particulate and keep them from flying in your eyes.
there is no tempered glass in an exoterra, i have drilled several. if you want a hole over 5/8 you are probably better off using a diamond core bit like the ones pictured at the reef place.
whatever bit you use you wear a mask, they both produce fine airborne glass dust which is a hazard for silicosis. a spray bottle can also be used.
already looked for the previous post but wasnt in my post history so i will see if i can find it in the archives.