Aftermarket Seat in Jetta

I am wondering if it would be unsafe to install a aftermarket rear facing third row seat in a Jetta wagon. My concern is primarily how far does the crush zone in Jetta wagons go into the cargo area behind second row seat. There are numerous seats on the market approved by the NHTSB. I know that Volvo's have such seats as an option and many SUVs have them as well. Third row seats in these vehicles don't seem much safer because of how close to the rear door they are located. Even minivans have seats right up against the rear glass. Anyone have any insight? I don't want to give up my TDI but need some extra seating.

It could be done. I compared the length of a Jetta SportWagon and a Kia Rondo that has third row seating and the lengths of both are 179". Check out the specs for both.
http://www.vw.com/jettasportwagen/completespecs/en/us/#dimensions
http://www.kia.com/#/rondo/specifications/
Hope this helps.
Franco