I was thinking about using something like a rubbing compound. Here is what one site said.
Using the Rubbing Compound
Rubbing compound is not normally needed when using the paint pen but you can apply it to the entire area to make the area smoother and shinier. Let the clearcoat dry for at least three days before using the rubbing compound. Use a clean, very soft cloth like an old tee shirt (for example DO NOT USE PAPER PRODUCTS as the wood fibers will scratch the paint!). Place a small quantity of rubbing compound on the vehicle and use circular strokes and apply even pressure to the vehicle. It's almost like waxing a vehicle except the rubbing compound is like an extremely fine liquid sandpaper. Buff with a clean cloth to a high gloss. (You may want to spray some paint and clearcoat on a smooth surface and practice to get the feel of it.) Sometimes lots of pressure is required to make the clear shine. The rubbing compound can also be applied by machine, but careful, it's very easy to burn the paint! You can get the same results by hand, it will just take a bit longer.