Try finding a smaller used main. Then tie enough line between the sail and the ring so that it hoists to the right height to fit into the boom. A older H-17 sail with a little delamination might be a good beater fun sail. Same thing with jibs. You can look outside the catamaran world to find a small storm jib. Something like a 470 or Laser 2 jib would be enough to help you about and not overpower you. Learning to tack a unirig is a skill that will help you in the long run anyway. Take a look at one of Rick Whites books on unirig tacking...it is fun once you get the hang of it. In my youth I even went to the extreme of sailing a H-18 in 45+ knot winds using my DN iceboat sail at 60 sq ft and had a blast.