I don't think you can do it without actually writing a program to fake the game out. For Warcraft III for instance, there is a program called battle.lan that does this by making the game think that the IP address your friend is on is actually a part of the local area network. It does this as an intermediary. Warcraft games are broadcast over the local network, and it takes that broadcast and sends it to the IP address you specify which also needs to which also needs to have battle.lan running. It then somehow broadcasts over there local area network your game and everything works. I don't know how this works or the technology behind it, but maybe there's something like this for risk as well.