Q&A

 Master

If your wheel locked with the key ON and the engine running, then I think the steering lock mechanism broke and you'll have to tow the car to a Beemer specialist. it's also possible that the brake/shift interlock is malfunctioning and jamming everything up. Good luck with it.
If backing out, you had the wheel turned and shut it off the wheel would lock, and you might have to grab the wheel and turn it a bit to get the tension off the locking pawl and allow the steering to unlock.
It sounds like the first possibility from your question. Here's a directory link for you:
http://repairpal.com/directory?address=32506&car_brand_na....
Can't you get a towtruck to lift the rear end? If so, no reason not to tow with the front wheels on a dolly if the wheels are too far turned to tow.. I can't see your situation, but if there's no other way maybe you do have to disconnect the driveshaft or the shift linkage but either means you'd have to jack the car and get under safely. Tough question. Some tow trucks have a winch and could drag it up on a trailer or flatbead but that's kinda brutal...