I installed an aftermarket Class III trailer hitch on my 4.4i like this one
It has worked very well for me on two occasions where I pulled a 5x8 U-Haul trailer and about 2500# of granite for 1000 miles from Texas to Wisconsin and Indiana.
The hardest part of the whole install for me was sourcing the OE wiring harness, which is NLA in the aftermarket or BMW. This harness was key to integrating the connector into the factory wiring plug in the rear hatch area aft of the spare tire.
Also you will need a brain box controller like this for your install to integrate it into the traction control and parking distance systems.
Here is the OE Westfalia wiring harness that I was able to find several years ago in new condition:
This is a very functional set up for me and it works well for my needs, others may choose to select a more OE set up.
Mike