As far as I know vehicles don't activate events yet, but you could possible make them fakeKill bricks when they hit bricks with enough force, and you can do it that way.
And to make it not completely destroy the whole tower, you can have a print brick or something set at 0, then every time the brick relays, add 1 to the print. When it overflows have it turn off the relay events for a moment and it should stop the propagation. All theory but whatever.
WRB852: Why was RTB 2.0 so expected? In my opinion it's pretty useless since it basically does what other things already do, but that didn't stop it from receiving a sticky did it? I think this adds more to the sandbox nature of Blockland extending the replay value, not to mention exploding stuff will be a lot more fun now.