You install Minecart Mania, and roll the minecart over a gold block. Really, as a server operator, I'd much rather people convinced Afforess to add new features to Minecart Mania than create new, conflicting minecart plugins.
I recommend that people post the errors and other troubles in the thread - I generally offer a 24-hour turnaround on an answer. But as to the OP's question, you could set the motion onVehicleMove, because you know the minecart is moving when it get's called.