Have you tried using Hamachi at all?
http://www.hamachi.cc/
I find that using it helps with some games and sims that are a bit shaky on MP, it makes getting Falcon working on MP a lot easier for example, and is useful on games where a central lobby is required for connection on occasions when the server is down. This worked for The Regiment, and helped a bit with server lag too, which is not a big issue with a sub sim, but a godsend with FPS and flight sims.
Having said that, I've not personally had any problems with SH4 on MP.