I'm not sure if what you want to do will work, just due to the way NAT works. Typically, you can't access NAT'ed services from the LAN side of a router. Because Blizzard chooses to route everything through Battle.net, this might be where your problem lies.
But as I said, I know Blizzard has a FAQ floating around and it should be able to answer your question. I googled for it, but couldn't readily find it.