What you are describing is lazy jacks. I have them on my catboat as well, not adjustable but loose enough not to interfere with sail shape and still control the sail. My sail is much bigger that an H-16 sail. The catboat boom is about 20' long and the boat is only 18'. I also have a topping lift. I know of some people who have adjustable lazy jacks so they can double as a topping lift.

One problem you might run into is that the downhaul would have to be slack or you wouldn't be able to get the sail locked at the top of the mast or unlocked to drop it.

Ideally it would be best to sail off the beach. I found how to get the boat on the beach at Emerald Isle last year and had a fantastic week sailing there.

Howard