what about water balast.. some bulbs at the bottom of the centerboard fill it with water and when its sailing it doesn't add weight until the bulb lifts out of the water then it adds the extra righting momentum you need....
It doesn't matter whether or not the weight is above or below the water - you're still adding mass to the boat that the sail power has to make accelerate and overcome the additional wetted surface area drag. Weight is weight whether it's neutrally buoyant or not.
