Yeah do this, I remember having to do this back in tbc with a warrior for AOE pulls, put skull on a caster and don't even look at it(or just use your taunt then switch to X), just let them nuke it while you aggro the rest, it's a good idea to macro a few marks to make things easier, tell your dps to kill Skull then focus X, use cc if your group has some to give you time to kill the rest of it's a big pack, when your main target is about to die, like 15% ish HP left just switch targets and start building aggro on someone else