Take Will in your party from level 3, have him summon the imp (turn invisible) and send it off to explore the goblin camp... Once it finds the portal just teleport the party in past the guards at the bridge
Oh yes. There will be variations on this too. I've just tried walking my spider familiar in (not invisible or sneaking) and the goblins can't talk to and don't attack it, and it can also get to the waypoint. Or you could just walk a party member turned invisible and do the same.
