The pilot and flight instructor were conducting a flight review when on the downwind leg of the airport traffic pattern the pilot reduced the throttle to idle to simulate an engine failure, but then inadvertently extended the flaps instead of the landing gear. While on short final, the pilot increased engine power to ensure that the airplane reached the runway and, as such, the landing gear horn did not sound. However, when engine power was subsequently reduced to idle before touch down, the pilot then heard the landing gear horn and the airplane landed on the runway with the landing gear retracted. The airplane came to rest on the runway and sustained substantial damage to the engine keel beam. The pilot and flight instructor both reported that there were no mechanical malfunctions or anomalies with the airplane that would have precluded normal operation.