Sorry I missed your inquiry a year ago, but short answer is most people don’t do it because no one makes a towbar faceplate for the Z3. I had to fabricate one from a Cadillac STS faceplate and raw steel plate, welding it up to fit the Z3 front subframe and bumper attachment points. Not a project for the faint of heart and would cost quite a bit if you paid a custom fabricator. If you really want to do it, pm me and I can send you pictures of the installation and graph paper layout of the plates needed to adapt to the Z3 frame when I get a spare moment.
Also, with an automatic trans, had to use a Remco driveshaft disconnect coupling. The Remco people and installers will tell you it won’t work because there is no room under a Z3 to put the disconnect linkage and carrier. I just made two 3/8″ holes in the transmission/driveshaft tunnel between the seats and pop two 5/16″ round steel rods down through them and throw the disconnect sleeve back and forth to disconnect/connect the driveshaft from the transmission. Easier than it sounds. The car is so small and the parts in that area are so close together that careful placement of the holes lets the rods just fall into place in the disconnect coupling groove. Pull the rods out after the change and set them on the floor beside the drivers seat until needed again. Simple as it gets. No cables, no adjustments, as the kids say “no worries”.