This topic brings up a question that may be a workaround for the OP.
With the eventual local co-op patch, you would in theory be creating a minimum of two characters. If you are allowed to mix and match multiplayer, (2 local at one of and 2 local at another) you would be able to create your full custom party.
All of this is built on many ifs that we do not have confirmation for yet, so take that as you will.
That being I know Sven gave his reasoning for not creating more characters than you have players. It was something to the effect of wanting players to focus on their character and origin for each play through.
