Well after my last post I wanted to try illuminating my surface from behind with a few IR LEDs. I found that with everything I tried, the LEDs just put way too much focused light on the surface. After talking with cerupcat on the nuigroup forums, he mentioned the use of the GamFusion material from www.gamonline.com as a diffuser of the IR light. The stuff is pretty cheap so I ordered some along with some more LEDs.
On a more exciting note, I came into some unexpected funding for my project. I can finally afford to buy a projector :)