Every year I have the same problem with carpenter bees boring into the back porch. During the winter I built an equipment shed and decided to use pressure treated wood on all of mainly for this reason. This spring I learned that PT wood is no deterrent to the bees at all. In fact, I think they discovered a new gym to play in.
Just thought I would throw that out if it helps anyone.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!