Sorry, but only European COMAND units have the TV/VIDEO capability. That is what the blank mode button is for.
I looked into retrofitting the TV system and it would require
tearing the interior apart and installing around 12 additional
control units and antennea modules. Huge $ too because the
modules total a couple thousand bucks. Then the system only allows you to watch when the car is in park. Take the shifter out of park, and the TV goes to a warning screen.
It can be done if money is no object however.