TacStar is making a do-it-yourself kit for adding a rubber grip surface to any smooth polymer.  It is called the Tactical Grip Coat.  The kit appears to be easy to use:

1. clean the surface
2. apply an adhesive
3. sprinkle on the rubber texture

The kits carry an MSRP of $19.95.  It is not clear from the site how much surface area each kit will cover.