Acura Integra wiper plug is the only one I know of...not sure if it fits on the 3's though as I have a Protege5, but it is the only plug that comes to mind...
Im sure home depot would have something you could modify to do the trick?
Why remove the rear wiper? Cleaner appearance?
My pictures (some have already seen). Home depot has the item, 3/4" plug in the hardware isle (drawers), bend to fit and use some silicone.
Looks really nice! Thought you mentioned it was a 7/8 plug? I'm hitting home depot tonight after work and spraying in my paint booth (aka my balcony storage closet).