Sorry to be a buzz kill but that is my nature.
I doubt that it is a good idea. It would be hard enough for that type of arrangement to work between good friends and even then you might not stay friends.
You might look at charter rates and try that formula or a variation with discounts for longer term use. A charter is really what you're talking about, right?
There is one exception. What about a live aboard who doesn't sail? It would be easy enough to monitor and, with a little courtesy, could work. Maybe they could sail with you.