Well i recently took a mate out who has never sailed before and he had the same problem but i had a non slip rale. I kept on trying to get him out on trapeze and yep he kept on falling back. When you go out on trapeze from crew bring the Jib Sheet (I know you have a short on but get a loger one) and hold on to that for support. This helped a fair bit but he still fell. The next time i got him out on wire i went out first and got him out so he could lean on me if he fell (its all practice). Keep trying you'll get it after a while.
If you are looking for a non slip product i would of suggested grip tape before i bought my boat. What you can do is go to a carpart store and ask for a strip which is like drip tape. The carprart will last longer, look better (if done right), feel better and best of all hold you better. I highly suggest the carpart but if you cant get any go for grip tape.
Well have fun and get out on wire as much as possible and just have fun.
cheers Jules