especially with the internet, we could have a dominikos situation where the MC does invite that person, but would that count? the MC wouldn't know who it is properly so it isn't an express invitation to a god, just someone who needs a place to stay
yes, that's the loophole. it doesn't explain the conditions in which the master invitation takes effect. so if via message or if the master must know who they are inviting are possible exploits. there's also direct contact, they could persuade the master in to taking them in, through a bargain of sorts, deception or even an honest request if the master doesn't see the harm in it.