Since the official servers no longer exist, even with the key for multiplayer you still would not be able to do anything.
On the other hand though, i saw people talking about Hamachi severs but i did not see anybody mentioning Tunngle so far. It works really good, even simpler than Hamachi as far as you ask me. Totally worth a try a true if you are looking for a way to play with friends of yours or other people.