For a WAN type connection to work you would have to live close enough to his house to get the wifi signal. The easier solution is to get his external IP (you can do this by just typing in google "Whats my IP"
Then find the port of his server (this will be in your server config file) then put his external IP separated by either a colon or semi colon, then the port number, no spaces.
If that doesn't work he needs to open up some ports and allow it through his firewall.
Or if thats to complicated you could always setup hamachi. Post back with any troubles you might be having.