Saw a guy around the corner from me once doing something similiar. Only it was in the driveway thay sloped down, so he'd parked at the top, had the rear wheels on the pavement and the front end 4ft or so in the air to make it more or less level. So if it had shifted, not only would it have fallen on him but rolled downhill. So a kind of twofer if the 2x4s failed.