I'd try to lap them. I saw some guy do it for his BMW and it worked really well. I've always read about lapping heatsinks for computers and it works like a wonder.
In other words, get a bunch of wet-dry sandpaper in different grits and start with the smallest number (the most coarse). I think these things go up to 2000 grit which is super fine. Finally, when you're done with that, maybe top it off with a buffer and polish... Now i'm not sure if that's good for plastic or not, but this is just what I would try.
You could probably google it and either find somewhere where someone has done it. I know the BMW one is out there somewhere. Anyways, don't f- up and good luck! =)