I've heard old LIRR engineers did this on occasion with the MP-54 cars, or, more exactly, throwing the controller from forward off, through emergency and into reverse off (yes, you could do this without popping the E brake if you were fast enough. I think dropping the control out of electric brake and into normal brake would, too. This is per the PRR's manual, though I imagine the LIRR units were much the same since the brakes were the same and this dealt with the braking features more than propulsion). anyway, clicking the contrtoller into reverse, switching, would flip the reversers on every car and then go into 1st point series.
This *worked*, but was bad for the equipment, as you now had a car that was effectively rolling backward and it's motors fighting with the third rail (which won).
The only use I've ever seen of 'plugging' in an EMU was in the Metroliners, GE version, where they actually threw the reversers and applied a controlled amount of electricity into the loop. GE called this 'catenary suplemental brakeing', and it could actually stop a car to 0 speed, and if the zero speed cutout didn't work, start rolling it backwards
The Metros were Silverliner derrived, but the Silverliners don't do this trick (the II/III cars didn't have any kind of dynamis/reg, the IVs used conventional dynamic, AFAIK). I suspect it wasn't very sucessful...The cars could also go through a series of normal dynamic steps, though the braking effort would vary with speed and contactor state (no camshaft), the supplemental braking was intended to smooth this out. None of this required any effort on the engineer's part - all of it was sorted out between the braking and propulsion system automatically. Usually...
(Yeah, I know, none of this deals with EMD or locomotives, but the talk of plugging remind me of it anyway...)
I'm guessing AC units know better than to allow this, and either just regen or ignore the engineer...