Siclick33,
The best way to do it really is to paint the airplane, however I get your desire to not have to do that. In that case, if the shapes you want to paint are simple, the easiest way is to mask the airplane off like you were going to paint it. Use the 3M vinyl tape (blue) to mask the edges the paint will go up against. Then (preferably) wet sand the gel coat that will be painted with 800 grit paper. Once you are done that, use a grey scotch brite pad right up against the tape edge to ensure the shine is gone all the way up to the edge. Spray your paint, I would use a razor blade to cut the paint line against the tape to reduce the risk or pulling an edge and then remove your mask.

Before you do ANY of that though, make sure you wash the entire airframe with a good unscented detergent with no oils in it for fragrance or moisturizing (tide powder laundry detergent seems to be the best). Then wipe it all down with a good was and grease remover like PPG's DX320 or DX330. Wipe the sanded area's with the DX320 again before painting.
Jeremy