Check out Carbox (German Company):
http://www.carbox.de/english/produkte_us.html
They have a lot of options for the 07-08 X5 including with the 2nd seat folded. Not sure if they will meet your needs or not.
Their U.S. Distributor is:
http://mats4less.com/carbox-floor-liners.html
Their website is not great but you call them they can order whatever you want.
Another option:
Hatchbag - The material is not real thick thus these tend to shift a bit during transit. Might not be great for an active dog.
http://www.hatchbag.com/suvcargoliner_hatchbag.php