I saw a setup that was similar to what palmwolfe describes.

Carpet wrapped 2x12's that were put in and out of the water. They had a "pin" (actually a short pipe) that kept the boards from sliding down off the wall into the water and buried a post a short distance inland from the wall. The post had a trailer crank mounted to it and was used to pull the boat up the ramps. When they were done, they put the 2x12's on dry land. The DNR didn’t harass them because it wasn't a fixed or permanent launch site.