Hmm ... I just finish my pens normally when working with PC ... I pretend it's wood and give it 6 - 9 coats of CA and go straight to finish sanding/polishing.
The only thing I've tried CA on where it didn't take was Alabaster (real stone)... It just sloughed right off when I went to finish sand. Could be that I need to give it a LOT more time to cure (like, overnight), but I'll have to try it again sometime.