Well, I doubt everyone is from a completely different universe. Probably at least two per setting. We might actually be able, if everyone is a major character, to smash forward just by having everyone name themselves and series. They grab a taken protagonist name, then it's like someone declaring themself cop, the real cop can out them. They pick some really second-string character, we know they'll full of crap. Bit of a blitz tactic, but we're likely to net someone that way, of course we might also out a role too. Still even if we don't name the character, it makes me more inclined to think that disclosing our setting might be a viable tactic.