Try placing a small piece of coarse sand paper, face down on the kit, and rubbing the back with the side of an exacto blade handle or piece of wooden dowel. This will you give a slightly roughened texture. Test it first, as you will need to practice the technique to get it right. I have heard some guys say they soften the plastic with glue first, but I envisage a stringy mess doing that.
Otherwise, mix some fine grit with paint and spread that on.