The flight instructor reported that the purpose of the flight was to provide a proficiency check out for the pilot, which is an organizational requirement prior to pilots being authorized to fly their airplanes. After completing area work, they returned to the airport. The pilot landed the airplane and taxied back to the departure end of the runway. The flight instructor then assumed control of the airplane for the purpose of demonstrating a rejected takeoff after a simulated engine failure. About 50 to 100 ft above the ground, he retarded the throttle, lowered the flaps to 40°, and lowered the nose. An excessive sink rate developed, and the airplane touched down slightly nose up, bounced, then rolled to a stop. A postaccident examination revealed substantial damage to the fuselage. The flight instructor reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.