I very much appreciate the replies, and it's clear there are a number of different solutions.
So I showed up at the boat with two furniture ratchet straps, the two davit extension arms that came with the boat, and a renewed resolve.
And i don't feel like i really figured it out. i think perhaps I should give up sailing. or at least dinghying.
Do you think, if you don't mind taking the time, post a picture or two showing how you solved
your issue? @enjaku, @Greene, how you mount those fenders? @timbenner, @faa50, your cool-sounding but complicated rigging
And thank you to @Scottster and @DavefromNZ for the pics (and so many other advicey things)