Trunk pass thru

I was looking for an almost-new C320 with nice extras and low mileage. One of the most important options to me was COMAND. Unfortunately, in C-class this limited the number of vehicles a lot. When I finally found what I was looking for, the car did not have the "Ski Sack w/Trunk Pass Thru" or foldable rear seat. Is it possible to add this/ these afterwards? Adding a trunk pass thru does not seem to be very difficult to do... Is it? Is there a place where I could buy those parts? I am in Texas.

-T