I'm reasonably sure that the hitch is not installed as part of the manufacturing process "on the line." There is no separate bumper cover, and I am sure they do not manually cut the bumper cover while assembling on the line, i.e., they probably install the hitch manually, after the car is completed, just like your dealer would.

It sounds silly that they would assemble the car completely, only to later remove the bumper cover manually to install the hitch, but for low volume options such as this, it actually makes sense to avoid any delays or additional complexity on the assembly line.

Many years ago when I worked for Ford, the Kentucky truck plant did low-volume options this way when truck customers wanted low volume options, particularly the larger commercial use trucks.