Ah yes, sorry you are right about the defrost.
It is entirely possible that if you looked it might be possible to transplant stuff. I was thinking there were extra items dictating a different liftgate, and maybe there is, but it wouldn't surprise me if there is some clever way to add the option without a special liftgagte.
I tried looking for some pic quickly but came up dry and my old 87 BII brochure doesn't show any so no help there.
A rear wiper is definitely one of the options I thought about because in the snow, all the road salt and moisture comes back up on the rear window and you can't see anything.