When I first got my car I was wondering what it would take to do this. I forget why I stopped researching...let me know if you figure it out.
EDIT: I found where I left off (link: http://www.zhpmafia.com/forums/showt...302#post445302). Sounds like you have to use NCSExpert to code our car to be seen as a convertible, and have an additional wire to the GM5 module.