XF 1.5 Force all users in a user group to use two factor authentication

I'm running Xenforo 1.5.15a and have a custom made user group. I'd like to force all users in that user group to have to set up two factor authentication the next time they visit the site. Is this possible at all?

Please note that these users have already registered and are already members of the user group so forcing two factor authentication to be on when registering isn't going to work.