Try Ironclad Online, add your friends' account as Friends and make a Friends only game.
You can also try Hamachi (hamachi.cc) and make a LAN game with the IP address provided by the TUN/TAP net adapter of Hamachi. If you use this way, both of you needs hamachi, in the same channel. You'll be assigned an IP address of the form 5.xxx.xxx.xxx (or something like this). Type in that address instead on the other side.
