Did this last year ... couldn't book as a through fare because of too long of a connection (4 minutes over max) and when checking in for the Mint leg the bags were checked straight through (SFO checkin). However we flew home out of BQN (which is a small outstation with contract employees at the counter) and we paid for the bag fee to head home (economy as first leg, connecting to mint).
You might have better luck depending on where you are flying from on the econ leg.