I used a foam-buff-pad, a 90-degree die-grinder and Novus Plastic Polish with good success. Didn't have any problem with "burning" the plastic, even at relatively high rpm, but I was careful.

I bought a Headlight Polish Kit from an Autozone, but the Novus Polish worked better.



Eastwood sells a product called "Autosol" which might do a good job too.

http://www.eastwoodco.com/jump.jsp?itemID=2621&itemType=PRODUCT