At least with the old postwar one I have(drawing a blank on the number) there is nothing terribly exotic about its operation-a magnet pulls down on the center plunger, which opens the hatches on the bottom.
The O27 "uncoupler" tracks that just had a single magnet inset into what was otherwise a standard looking section of straight track would probably work best-I think Lionel and K-Line both made them.
Honestly, though, the coal ramp is the most trouble free way of getting this to work as it is totally open under the car aside from just the small magnet set into the center.
I have used aquarium gravel in mine, but find that it tends to "leak"(although the coal loader I have sitting under it seems to feed the gravel a bit more reliably than the Lionel chunks of plastic, which it tends to throw everywhere).
