The pilot stated that he initiated the takeoff as normal. However, as the airplane accelerated through 80 knots the nose lifted "abruptly." He could not move the control stick far enough forward to lower the nose and level the airplane. As a result, he elected to reject the takeoff. The pilot used elevator trim, which lowered the nose enough for landing. The pilot reported the airplane touched down on the runway, but with the left wing low. The airplane drifted to the left and departed the runway pavement "at a shallow angle." The nose wheel steering had been disengaged during takeoff roll in accordance with standard flight manual procedures. As a result, the pilot was limited to differential braking to maintain control. The airplane encountered wet grass adjacent to the runway, and subsequently struck a runway sign and a light before coming to a stop. A post accident inspection revealed that the right front (co-pilot) seat belt had been buckled around the flight control stick, out of sight of the pilot, restricting full movement of the controls. The airplane sustained impact damage to the left wing, including the leading edge fuel tank and wing ribs. The pilot commented that he removed the co-pilot control stick to eliminate any possibility of a similar event in the future.