It is extremely difficult to do this. Initially I purchased a mirror with just the FLA camera thinking to add it to my exisiting mirror which already had EC/DWA/GTO/Compass but after opening up the mirror, the entire circuit board is different. I ended up selling and purchasing a mirror which had the following options
EC - Electrochromatic (dimming
DWA - clown nose for alarm
GTO - Grarage door opener (home link)
Compass - self explanatory
FLA - Fernlicht assist (auto high beam)
https://xoutpost.com/bmw-sav-forums/...-retrofit.html
If you are going to do it, make sure you get a mirror from an E70, not an E65 which has different options within the FLA and doesn't work properly with the E70