They make floatable extensions for jonboats that stick out beyond the motor and are flush with the boat sides. These are a dealer item and they are made special for different models, particularly jet boats to raise the back end up. If you knew someone who could weld and fabricate these extensions, that might be a way to go.....probably expensive. Other than that, outriggers for canoes may be adaptable. If you really need the flotation, a couple of fair sized inflated boat fenders might work affixed to the hull....would slow down the progress through the water, but would add flotation.