Actually you can simplify my suggested technique by just pulsing the transistor you are testing. Use an analog switch, controlled by a pulse generator, to switch the gate voltage to the MOSFET under test. (Note: You need to add a low value gate-source resistor to discharge the gate capacitance when turning the transistor off, or use a gate-driver circuit to reduce the turn-on and turn-off time). You probably should also add a snubber series RC circuit from the transistor drain to source to minimize spikes from stray circuit inductance.