I saw this thread in passing last week and then guess what I found in my brand new front and back porches this weekend? I never heard of carpenter bees until I moved to Virginia.
I tried the wood putty plug and they either knocked it out or it fell out. Normally, I am afraid of bees, but I was so mad that they were eating my brand new remodeled house that I was ready to grab one and strangle it with my bare hands!
I'm going to try Bondo this weekend to plug the holes.