Really theres nothing that i can think of that will remove the dip but wont harm the wheel. Paint stripper is gonna eat right threw the dip then start to bubble the finish on the wheels, which will then start to flake. i can imagine you want that to happen.
i would have a go with the power washer, since you now have areas of exposed rim. Wish i could be of more help
ex. ITS RX-7
currently OMS D-sport racer
DD: 05 zx3, Stealth CAI, AL 103's, 17x7 Enkei EV5's