As stated by LaughingLeader and Baardvark, the game doesn't work like that, and it would in fact be very difficult to implement if it's not already.
As for your notion of just randomly joining multiplayer games and being assigned things by randomness... Well, a lot of people don't realize they can turn off the ability for random strangers to join in on their games, and so just kick said strangers.
The system as it is now works fine. Join the game with your friends while they're in character creation.
As for saying that it's 'pretty simple' to do something a completely irrelevant game series did... Well by all means, then! It being so simple, use the modding tools and make a mod for it so that you and all your friends can use that system!
