Removing Porsche primer

[Auf los!]

I'm involved in a project to have plain, black plastic side mirrors. Wanting to retain my regular painted ones, I ordered a set of new mirror housings, but they come primered with white paint. I want to remove this primer without "crazing" or otherwise damaging the black plastic of the housing. (I scraped off some primer from the inside to make sure the housing is black plastic, and it is.)

This white primer Porsche uses is incredibly tough. To remove it, I have tried soaking the housings in brake fluid, lacquer thinner, oil-base paint thinner, denatured alcohol, and acetone. None of these have had any effect. I'm stumped!

Anyone got any other ideas? Thanks!