I don't have much to say that would help you, but I've been working on figuring out the same thing.
I feel like this should be possible within the editor. I began by opening CharacterCreation level of the "Main" and trying to figure out what entity was generating character creation. A few things I think may be necessary, for one, adding StartPoint triggers for characters 3 and 4 will be necessary.
The roadblock I've hit is trying to figure out what entity generates the menus and the ability of these menus to change the player models shown on the screen. I feel like this stuff might be related to the "FON_CharacterCreation_A_***" items. If you open up the items list you'll see these entities positioned slightly below the level where the player models are standing. I've tried deleting all these and really everything around where the character models are standing to see if I could break character creation, as that would let me know what controls it. At this time however even with all this stuff deleted the character creation screen works.
If someone else figures out a clue or has any idea what controls this, I'd love to hear it.
