In commercial incubators, the buildup on the top is not usually a problem because the eggs themselves are often contained in small containers with holes in the sides and a secure lid on top.
If you are concerned about humidity, the best thing to do is line the bottom of the lid with a towel and change the towel out every time it gets very wet.
There are commercial ways to regulate humidity much like many of us regulate temperature. But going this route is usually unnecessary and expensive.