I actually had an iBook come in from a school, who so nicely gave it a tattoo with their school name poorly scrawled across the bottom of the ibook. I never got the damn marker off unfortunately.
Anyway, flux remover might work since it will eat away at the rubber, but chances are it will take eternity and will probably damage the surface. Flux remover on metal is perfectly fine and will remove just about any type of glue or marker. Isopropyl alcohol is far less damaging than that stuff, I have almost no reservations using it unless on low quality plastics, it just doesn't work for set in marker.