I know you said "other than paint", but its worth mentioning that I have had VERY good results using Krylon Fusion for plastic Satin Black paint. I've done belly pans, dash pieces, and gas tanks. The satin black paint makes them lool like the orignal paint. It DOES NOT peel or flake off, but don't spill any gas on the tank!
If you try the plastic renew products mentioned, take a before and after picture and post your results.