If I was sitting beside you I suggest that you move. If you have to use the extender seat belt you're likely incapable of assisting in an emergency. The point of being in that seat is to get the aircraft emergency door open as fast as possible. Your size my preclude this and, therefore, you are duty bound to exclude yourself from the job. Safety is first and foremost when flying and there can be no compromises on that point. If you're so huge that your girth spills out over the seat, call AC and request a second seat for the 50% reduction. Why Fly is right, Canada has deep socialist traditions and the Canadian Supreme Court recently ruled that obese PAX are entitled to discounted seats to "reasonably accommodate" their size. I would save yourself the hassle and change seats.