@ Derek, ty for reply. Even with a cooldown...I think you could just use normal counter spell untill cooldown is off, and then spell leech. You can reduce the cost of counter spell to virtually nothing with buffs / traits. Or you could use more than one mage, etc.
It'd obviously be more of a hassle, but you could still do it. It'd be a temptation to stay in tactical longer and just drain a mob, even though its really boring.