I know it has been done using one of my RCS - BELTROL R/C ESC's but I have not seen pics of exactly how it was done.
As I understand it the loco in question is pretty basic, so really all you need to do is isolate the track pick ups and feed the ESC output into what were the track pick up wires.
For those that feel confident it should be pretty easy to isolate the front and rear lights to permit constant brightness directional lighting.
Sound triggers as well, if you need them.