The only thing i can see as a magic tank at range is some sort of projection type. You probably summon a "pet" and that pet will go to the boss but your character far away is actually taking the damage, the pet would be only a place holder. Maybe make it have a link like sch have with the fairy and if that link is broken the "pet" vanish and the boss will go to the second in the hate list unless you summon it back. the only thing i would see the pet doing are auto attacks and any defencive cooldown you use, the rest would be your character.