I think he's in it for the long haul, sadly.
I've no idea how they're going to work it into the nominations process over the series as there's no way for a remotely fair round of nominations if HMs are being tricked by the producers into self-disenfranchising their votes cast for Michael (as they clearly won't count), ensuring a false result, unrepresentative of the will of the electorate.
There won't be a single set of nominations in the series that won't have been essentially fiddled by the producers to get the result they want - which is to keep mole twist going.
He can't be head of house every week. I mean, he could be, but they'll struggle to swing that without blatantly outing Michael's status.