I would make a cage for the ball, say a hollow tube that the metal ball fits within. At both ends of the tube is a pair of contacts (say made with paper clip wire) that the ball shorts out, completing the circuit and energizing the LED. Bend the tube slightly so that when the tube is horizontal, the ball becomes positioned away from the ends of the tube via gravity, where the tube dips down . When vertical, the ball shorts the contacts at one end of the tube, or the other. Of course, if you flip the tube all the away around so that the dip in the tube is at the top instead of the bottom, the ball will fall to one end of the tube, even though it is horizontal. You would want to avoid doing that, if possible.