Discovered this today in Zul'Gurub. You can remove the Lightning Shield buff from the guards without aggroing. Just spam Snowballs at them. You'll take damage each time it procs and uses a charge, but keep doing it and it will use up all the charges.
Haven't tried this on other mobs yet, might be worth giving a try.
[edit: Odear (lower in thread) tried this out on mobs in the Elemental Plateau and reports that it works on them too!]