I'll need to have a play... Got a copy of the latest MMI firmware for the A7 (it's on K0770 I think at present, which is newer than the original as it added the Audi Connect stuff) and find out if it can be enabled.
What I'm really interested in is whether the new MMI version that's coming in the facelifted A7/A6 soon which has the Apple/Android screen mirroring tech is just software or hardware