Unlocking the steering wheel

Good question. For loading/unloading purposes, if the wheels are straight and you align the car and the trailer, you could always push it up on the trailer (a winch would be a better route). Once you unload it, and if you haven't figured out how to unlock it yet, you could use a cheap pair/set of wheel dollies/skates to manuever it around. This is a temp fix but one that will get the car moved.