polishing out pits

Ok i had customer who came in today and wanted to get a couple guns blued but he doesn't want any pitting to be on the gun. Usually we can work out most pitting but this gun has some pretty deep pitting. Nothing to make it unsafe but enough it can't be polished out without leaving a low spot. I was wondering if anyone had as way they filled in the worst spots to build them up. Any info would be great.