The instructor pilot stated that in order to simulate an engine failure, he turned the fuel selector for the right engine to the 'off' position. He stated that at some point during the approach to the airfield he returned the fuel selector to the 'on' position and restarted the right engine. He left the power on the right engine at a low power setting, to continue to simulate a failed engine. At about 30 feet a go-around was executed, and both engines responded for about 30 seconds. After 30 seconds, the right engine failed and the aircraft would not climb on one engine. In order to avoid power lines, the pilot elected to attempt a forced landing in a field. During the forced landing the right wing contacted the terrain and the aircraft crashed. The aircraft pilot's manual states that single engine demonstrations should be accomplished using the power and propeller levers and should be accomplished at 5000 feet above ground level.