I don't know how to do this, but is it possible for a unit to transform into another unit while using bladestorm? I would like to make the unit transform into the tornado model while using it. I was thinking making like a Metamorphasis with the tornado model and permanent immolation. But there should be a better way to do it...
You could hide the casting unit and create a tornado in its place, or you could request for somebody to replace the Bladestorm animation with a tornado.