I know of a few things you can do to help preserve your supercharger and prevent internal engine corrosion / spark plugs rusting. I don't profess to be a mechanic, just what I have learnt from others:
1. You can actually put a bit of dishwashing liquid through when fresh water flushing. This helps break down salt crystals and clean out other grime. They key afterwards however is to make sure you get all of the water out of the pump and not have it sit in there, as it can condesate through the exhaust and up into the cylinders (rusty plugs). This means you should start your engine dry (without a hose) a couple of times in the days after flushing to get any remaining water out. Just for 10 seconds or so. You'll be surprised how much water still comes out!
2. You can also fog your supercharger after each saltwater use and when storing. On my Kawaski I just put a small hole in the air intake hose and stuck the fogging oil spray can directly in there with the engine running. To seal the hole I just used a small threaded valve.
3. Lastly, and this shouldn't be necessary IMHO if you do the first two steps, but you can remove the spark plugs in between rides.