Among other things you will need to figure out... The original compresses down to very thin and bends/forms where it goes in the side moulding, under visors and mirrors etc. A hard board may crack if it works at all in those spots.
Have you tried to locate a used one? As long as its near complete and not severely warped, probably a lot less work to repair one. I'm very much a DIY penny pincher, but if I was not able to repair mine or find one, this is one part where I think I would have dug deep and bought one.
