i dont think there would be a way to do it with out damaging the black parts.
you could try tapeing up the black parts and wetsanding the damage then reclearing the wheel but you could have problems with the edges and you would have to be spot on with your tape lines.
he could have them powdercoated and will run about 150-200 a wheel and they dont look like really pricey wheels so for that price he can just get a new set.
i have seen aircraft striper used on factory polished/cleared wheels and all the clear would come off then the wheel can be polished but if you do this that black would be gone.