All the Kammback ideas I've tossed around in my head for use on my Jetta always end up with some kind of permanent hing/pin locations added to the body. Though my car is 20 years old, and its sole purpose in life is eccomodding.
Attaching to the trunk lid wouldn't work so good for me because of my WVO tank in the trunk. If I ever do make a Kammback, it will have hinges made into the roof where the rain gutters are. This way the Kamm could lift like a hatchback to give access to the trunk lid and allow it to open.