One "easy" way of "writing" is to answer support emails / calls. It is almost the same as teaching stuff, only with a more relaxed timeline. I am currently supporting a system (and have been supporting other such systems in the past) about which I know very little. So each time a support request comes in I have to dig, understand, formulate an answer, scrap it, dig again deeper, ask around, etc.

In the end I don't even care if this takes a lot of time, I learn so much in the process that it is absolutely worth it. I would not be happy doing it 100% though, because writing code is really on a different level, but I find that these two complement each other very well.