http://ecomodder.com/forum/showthrea...back-7577.html
Here is how I did mine. I didn't want to drill into the car either.
http://ecomodder.com/forum/showthrea...tml#post100224
Here is how I started my partial boattail, attaching to the parts in the first link. It was originally going to just be a kammback. You might be able to do something similar.