IIRC, the BMT standards received a (or utilized an existing) 9-pin portion for MUDC. The ones which were coupled into B units had the button consoles in the two end cars deactivated. The conductor still operated the doors from the center console of whichever car he was stationed in.
I've said this before, but in the two years I rode on the BMT standards regularly, I NEVER saw the conductor at a button console. The only reason I can think of was that somehow I never happened to be in the second or fifth car of any train. They always ran in 6-car trains on the Canarsie. Here's the real kicker: I do remember seeing what appeared to be the conductor in the motorman's cab of the fourth car on one occasion after getting off at Lorimer St., and as a result, came away with the mistaken impression that the door controls were relocated to the cabs.
I stand corrected in advance if any of this is wrong.