Fummins - You really are a genius. I've mentioned a few times about letting a car roll off a cliff. To get rid of it in a creative way. But, I know of no cliffs around here that are substantial enough to illicit the kind of drama and damage worth bothering with. And if I could find one, there'd be a guard rail making it impossible to roll off. Think the last 2 minutes of the movie Duel.
However, your idea to "leave it on the tracks." Now that is something very feasible. That would take care of disposal. Wipe down the fingerprints, remove all vin information, and "leave it on the tracks." Viola. Disposal complete. You're a genius!