1. find submerged reef/rocks/whatever away from any existing country.
2. dredge it up above high-tide.
3. make it a separate nation.
4. create giant floating island.
5. floating island is considered a ship -- choose nationality of ship to be same as aforementioned island.
6. you now have your own floating island to do whatever with. make more. put them together. you choose.
That sounds like a pain in the butt, doesn't it...