My bike did that last season. Here's what worked for me:
1. unbolt rear caliper
2. hold it up as high as the hose will allow you to.
3. stick a paint stirring stick or anything as thick as the rotor, between the pads so they don't come out too far.
the idea is, air bubbles like to rise naturally. If the caliper is below the master you are trying to fight the bubbles by pushing them down to the bleeder.
By raising the caliper higher your pushing them in their natural direction.
Good luck & welcome to the board.