I did this a few months ago, it was very awkward because we left them in place. I ended up using a 1" foam brush and even a small art brush to get in the edges. I asked the guy at the paint store after the fact and he told me that it is worth the effort to take the rails apart and then just use a small brush. I have to agree with him. The best way would be to send them out to be sprayed, if that is an option.