At that time of night, there are three possible options:
1) If any park is having EMH, take the bus/monorail to that park from the Poly, and transfer to the Beach Club bus.
2) If there are no EMHs operating, take the bus to Downtown Disney from the Poly and then transfer.
3) Have the concierge at the Poly order you a cab. Don't know how much it'd cost, but it would be your fastest/easiest option.
Good luck, and I promise that you will not be stranded!