How to paint a raised surface

[DD931]

I'm looking for advice on how to paint a raised surface - the challenge is an aftermarket radio with raised letters on the plastic faceplate. The letters need to be painted. The faceplate is off the radio and is flat. Tight nap roller? Some sort of felt rig? How about laying down a coat of paint on a piece of cardboard that you lightly dip the piece into/onto? Of course my fear is applying too much paint and having a crappy mess when I'm done. I'm out of ideas and was hoping to gain from others mistakes before I have to learn it all the hard way!! Thanks for any help you all can offer!!!