There's a thread of one using the plastic of an old cassette case. You don't need anything as thick as 3/4, I think about 1/8 should do the job. If you go to Radio Shack (or something like it) they sell sheets of 8x10 ABS plastic that are rigid but can be cut pretty easily.
Here, I found the thread. Scroll down to the bottom.
My Installation.... in one week! I hope...