It would be a long shot to get a permit to build a concrete ramp into the water. However, thinking outside the box: you can get a permit to build a boathouse. So, if you build a boathouse big enough for the plane’s wingspan, then you can put a rotating lift inside the boathouse. See link below for an example. Sunstream had a dealer on Winni (Watermark Marine), so this concept might be something to consider. Good luck!
http://www.liftguy.ca/portfolio/plane-lifts/