The aircraft owner was taking multi-engine training for a class rating. He stated that the CFI told him not to use the auxiliary electric fuel pumps during takeoff, a procedure in contradiction to the flight manual. During the takeoff ground roll, the student said the right engine quit at a speed just below rotation. The CFI assumed control of the aircraft and continued the takeoff, lost control of the aircraft, and landed in a field off the departure end of the runway. The student said the aircraft was halfway down the 3,400 ft runway when the engine quit. The flight manual lists Vmc as 82 mph, and Vyse as 109 mph. The takeoff and landing ground roll distance charts in the flight manual state that 960 feet is required to accelerate to 86 mph, and 650 ft is required to decelerate from that speed. Examination of the aircraft revealed that the right propeller was not feathered, and no reason was found for the right engine power loss.