Can you fumble backwards out of bounds on purpose?

This may be a dumb question but, I was watching the end of an old game between the Steelers and Browns.The Browns were down by a field goal and driving. The reciever caught the ball in the middle of the field and tried to make it to the sideline before the clock ran out. They had no timeouts. Could he have thrown the ball backwards out of bounds and stopped the clock? I know there is a rule about fumble on purpose to advance the ball but never heard if you can fumble it backwards.