Don't be technical when it comes to safety. This would have been an obvious foul if the QB had not released the ball. Just because he did does not make it any less dangerous.
If you think he still had the ball when it started, just make it a horse-collar tackle, just as you would do if he fumbled as he was being pulled down. If the ball is gone, make it RPS ("...throwing the passer to the ground after the ball is gone.") A supervisor would be foolish not to support it.