I have added electro couplers to a couple of Weaver brass engines, an 2-8-0 and 4-6-2 but it required a lot of fabrication. I doubt one could be added to a diecast engine without having it stick out a 1/4 mile due to more metal in a diecast frame.
The proximity of the pilot truck to the pilot is what prevents installing an electro coupler.
Pete