http://www.e90post.com/forums/showthread.php?t=315379
I've seen a few others but can't find them. You can either do this free-air or with an enclosure behind the woofer. I would think though that the W7 is not well suited for IB.
If you do this you need to make damn sure that the baffle is sealed to the ski-pass meaning there can be no air gaps between the trunk space and the cabin.