Loggerman,
I hope that whatever you fly in the offshore environment has emergency or fixed flotation. I spent a fair number of years in the GOM and as an Army instructor doing autos. In the oil patch we used a B206 with fixed floats landing in the water to small lakes or ponds for practice. The military didn't have floatation. The drill was to plan the deceleration a bit higher than if landing on land (about 75 feet AGL). The altitude would also help should you miss judge you height above the waves or swells, which could ruin your whole day if you hit them while they were rising.
Without floats - I believe that after touchdown you would hold as much up collective to disipate the rotor. Wave action and/or wind dwill more than likely determine the direction you will roll. Which ever way it rolls let the rotor stop. Then exit. Consider unlocking or opening the cockpit door latch while in the auto. This is just in case you hit hard and jam the door making it difficult to open once on/in the water. The door will not flop around while you autorotate with forward airspeed.
It's been a long time since I had to think about flying offshore without floats. Not good for longevity, especially if your flying a single-engine aircraft.
Good luck