Sorry, my cp and bottom cabinet are flush. I have a black curtain down there, but it blocks the IR. Either that or legs aren't hot enough.
I also tried my best to disassemble it, but decided I couldn't do it without breaking it. Got the cover off, but the front plate is riveted to the circuit board.
You've got me thinking of opaque materials though. I don't know if I want to shell out the cash for custom glass, but I do know how to frost glass/plexi. You just brush the stuff on and let it dry.
You think it would look better 100% frosted or just the portion for the sensor? or maybe frosted 100% and paint over black the frosted section away from the sensor. Keeping a constant texture.

Biggest problem I'm seeing after playing with it is that the sensor needs nearly a 180 degree field of view. If I just make a hole so it can see straight forward, it is much less sensitive.
Here's an idea, let me know your thoughts. IR filters can be found inexpensively as developed unexposed camera film (blocks visible, allows ir). I could use it like pin stripes in my design and place the sensor in any of the areas. Various widths would be available; 35mm, 120mm...

I am also ditching the monitor being powered by it. I reset the time to only stay on a few seconds to test and it can't detect a person standing so close in front of it after the initial detection. Doesn't matter how much you move, you're all it can see and there is no contrast. I also worry that when I switch from my current crt to an lcd monitor, the lcd monitor won't turn on when power is removed and restored.
My idea now is to plug a dc adapter into the spike strip, run that up to an opticoupler and use that as an input to the keyboard encoder, bringing the computer out of power save. It would be an unused key, but I worry about the bios or windows complaining that a key is being held down. I'll have to give it some more thought.