Feeding in their cage is the best. Yes you have to be careful and make sure that they don't ingest too much aspen (some if fine... Mouthfuls isn't)
BP's don't get more aggressive when you feed them in their cage. All of the big name breeders and many people on this site feed in the snakes cages, including me.
unless you look/smell/and are about the same size as a rodent a BP isn't going to mistake you for one.