Baloney... As long as you have at least an SE, you can do the conversion. How do I know?
I did it.
Cost me $500 at an aftermarket shop. I tow regularly and the BT mirrors are great.
Oh, and check the aftermarket shops; often they can get the same mirrors for less.
In my case, the dealer quoted me $1,000.

I think they just didn't want to do it.