not an option on US cars, but I just stuck one in the M5...
I had always wanted to throw one of these on my old 89 535 sedan. Now
that I have the blk/blk M5, I have more of a need to keep the sun from
beating directly on the seat backs. Non-US parcel shelves do not have
the 3rd brake light molded in the package tray, so I had to scavenge
the sunshade from a Euro shelf and cut the opening in my parcel shelf.
The thing needed to be recovered to begin with, so I went to town. $75
to have the shelf covered in a nice material that was a bit thicker
than stock material. There is one area that did not turn out perfect,
but overall I cannot complain. Although the original material was
anthracite, I figured that would only fade again. Since my black
interior is an early build, my carpet, headliner, a-b-c pillars are
actually gray. I went for the match with this fabric color choice.
http://www.hersted.org/M5%20sunshade/