The certified flight instructor (CFI) and student pilot were performing a short field landing in the multi-engine airplane. The CFI reported that the student pilot was at the controls, and performing a stable landing approach. During the landing flare the airplane banked 30 degrees to the right and the CFI attempted to apply corrective control inputs. He stated that the airspeed, altitude, and bank angle prevented him from performing a go-around. The airplane landed, departed the runway, and came to rest beyond a parallel taxiway. Post accident examination revealed damage to the right aileron, and creases in the upper wing skins, adjacent to the right engine. The CFI stated that there were no mechanical malfunctions of failures of the airplane, and that gusting left crosswinds existed at the time of the accident.