Actually, I came to conclusion that current 'strafe to cursor' while button is pressed is best.
Sometimes you need to very quickly perform single action like teleport with Hyperion or block missile approaching from rear with omnishield. Just letting shift go for split second is faster than toggle off -> do your stuff -> toggle on, and less error-prone.
Plus, shift doesn't count for keyboard key rollover (on almost any keyboard) and it's not like there are any other keys to conveniently press with pinky.
Still, just having option to toggle (not as default) wouldn't hurt.