Back in the Olde Dayes when I used to build car models, I'd brush clear lacquer on the seats and floor to "craze" the plastic and create a fabric-like texture to paint over. That was more than 20 years ago, and I don't know if different chemical formulas these days may affect the...er...effect, but it might be worth a shot on a piece of scrap plastic to see what happens.
Honestly though, the sandpaper thing is probably way easier to deal with :lol