There is no such car as a BWM, but many BMW's have been made.
Remco says the only way to tow a 99 Z3 is on a trailer.
With that said no one makes a base plate for one.
You might be able to tow it 4 down if you make your own base plate. Take the driveshaft off when towing.
Or maybe you can get
this company make a disconnect for it.