[Greg Reid]

You can use a brush...I've done that kind of stuff with a small brush for years...you just don't worry about trying to stay inside the letters. Cleanup around the letters the same way you would clean up the overspray. The same way these guys described it above.
Your idea of the sponge would work too. I've even used a wooden kitchen match, a toothpick etc.
Lots of ways to skin a cat.