If the shutter speed is 1/2 sec. it should not require compensation. I have always felt that Zone II is fixed for any specific film regardless of ultimate subject illumination. Maybe I'm on the wrong track here and/or have misinterpreted the requirements listed in your example, but if I was to do this, I would photograph a gray card (or my palm?) with the camera set to produce a Zone II using whatever light is available. If the time setting is longer than it seems practical, try to get more light on the card / hand.