Yes, it can be done. Surprised that they said they couldn't. You just mask off what you don't want to be coated. You can look at the beginning of this thread and see how the edge of the rim was masked off. But yours would be masked off more. If they are worried about stripping the current powder coat off and harming the polished lip, they could use paint stripper and the coating will have a "melting off" appearance than wrinkle off like traditional paint.