One time non-roster player in league play

Does anyone know the rule about non-roster players during league play? I have a friend from Charlotte coming to visit for a week and I wanted to know if he could play on my team for the July 23rd games.

No official rule

I don't think that there is a standing, official rule, but if history is any guide, then you have nothing to worry about.
They'll find a place for your friend.