Aaron, just the plastic mount or the whole damn shifter?
If it's the plastic mount, and they won't cover it under warranty for some reason, buy the mount from the parts counter. It's like $20 and it's super easy to swap out, only takes about 45 minutes and a few common tools. If you're taking it to St. Johns Ford though, I'm sure they'll just do it for you with no problems.
Just tell them you're having too much fun picking up my old parts.