Recently on my Audi S5 I used a package from NavTV that consisted of front and rear cameras as well as the control module for integration to the existing MMI. Granted this was a professional install as I was looking to achieve OEM functionality. I would like to do the same to my Boxster, but as a purist, I don't want to replace the CDR.
You might want to check out NavTV...they have done some pretty cool stuff, and have a huge range of products (including a FLIR camera, which I seriously considered). If you do find that they have a solution for a 986, I would be interested in using them again.
EDIT: after posting, I looked at their site and saw that they have an LCD overlay/rear view mirror combo that would allow a camera input. I might be seeing a future purchase/solution for me.