How about a dipole?
Since you don't have a backstay, you could build a wire dipole (with traps to cover a couple of bands), and hoist one end to the top of the mast with a spinnaker halyard and tie the other end to the stern somewhere. I think it would work like a sloper with a pattern off the aft end of your boat. Wouldn't need a ground system, but you would have coax going to the center of the antenna. When not in use, just take it down and roll it up.Just a thought.Ken Palmer, S/V LibertyW2IMO