I don't think it's possible to add factory nav if you don't have it already. Somebody did figure out how to do this to a mustang. This is off of a Mustang forum explaining how to do this.http://themustangsource.com/forums/f...em-nav-516988/ I wanted to do this to my Mustang but it was not worth the time or money. Easier to do aftermarket.
You'd probably also have issues updating the factory head unit and getting the firmware for it once installed. You'll need to update it whenever they release the update fixing all the broken Sync "features" that were broken in the last update. Then you'll need to update again to fix whatever gets broken in that future update.
For what it would cost, you could get a way better head unit aftermarket and put that in.
I have a 2009 and ordered one from 4DTech. All the wiring and parts are included. The issue is there is currently no factory navigation replacement for the 4.3" screen models, which is what I assume you have. Therefore, aftermarket is your only hope.