If you're feeling adventurous, you could try an old-school lava blade. Hard to set up though.
Obligatory "turtles can do everything" statement.
Also, if you switched out that lever with a button, then you could have a crusher on a timer. Unless you have that lever hooked up to the spawner too. In that case, still have a button, but have a latch or toggle somewhere along the line.
Redstone can do *almost* everything. Although it's kinda hard to do without redpower, so have a backup system planned in case that doesn't make it into the next update.