I believe that you could do that by creating an item spell/ability that would have a ranged attack of it's own, seperate from your main attack. If you have ever played the game battleships, this is how all of the items work in there, the items have their own attacks, rather than the unit. With orbs, they do the same thing, except that the attack makes it so that you can only attack air. So pop open the orb of choice in object editor, and see what abilities it has. Once you tracked that down, modify or create a new ability based on what you found there, and that should allow you to do it.