I have not, however I seem to recall Details West made an add-on backup light....found it, part #BL-162 Pyle backup light for E and F units. You would have to add a bulb or LED behind it. There's also a few manufacturers that make add-on ditch lights that are wired with LEDs installed, such as Rapido. I'm not sure how close those are to the prototype, but you might be able to make it work with a little modification.
From a prototype standpoint, it looks like backup lights varied by railroad. Some had them, others did not. A few had portable lights that crews would hang in the rear doorway or attach to a handrail for reverse moves. I seem to remember reading somewhere that they even had ones that could be plugged into the rear MU receptacle and turned on and off from the cab.