Down here in Shreveport, the shoreline around our club is completely bulkheaded. We have no beach to launch from. Our solution: ramps, similar to the one you've described. Based on my experience of sailing from a ramp for the past four years, I'd like to make a suggestion. I don't think the idea of using 4" rollers is the best way to go. They'll be difficult to sail up on with any consistancy. If you try to do that, you'll likely fall of the edge of the rollers more often than not, quite possibily damaging your boat in the process.
We've come up with a very effective ramp. It's made of wood laid across a metal frame. It measures 24' long by 12' wide and is hinged to the bulkhead with huge hinges. We've carpeted 4'x8'x1/2" plywood sheets to use as runners to slide cats up and down the ramp. Sliding the Hobie down a pair of four foot wide runners to launch is pretty easy. We recover by sailing right up on the carpet. Just make sure that if anyone with a daggerboard cat uses it, they remember to raise their boards.
Here's a couple of photos:
Side note - I just bought a lightly used six-batten sail, Fantasia pattern from 1986. It's still a little crisp, looks great.