My friend and I have managed to get multiplayer kinda working by blocking nwmaster.bioware.com in our hosts file (setting the address to 127.0.0.1) or if you have other software for blocking addresses, try blocking that one. It won't let you on servers that aren't blocking it, but at least one of you can host and the others join that person.
I am very interested in setting up something like that.
I have to block the authentication server using a firewall and then one computer hosts a LAN game and the other simply joins?
Pretty much. Both computers need to be blocking the master server in their firewalls, or if your router lets you do such things, you could just block it at the router if you're all behind that router.
Odd thing was it worked when one of us hosted but not the other, and I don't know why. So if it doesn't work when one person hosts, try the other person hosting.
I also think it might not work if you both are still using identical keys - we tried this when I had already gotten my key but my friend had not. Maybe (cough) come up with a different key somewhere for one of you, or wait until at least one of you gets new keys.
But, on a lighter note, my friend's key finally got here today (took 6 days total) so we don't have to fool with this rigamarole any more :P we can just play normally.