So I got 3 ideas to work with so far:
Barbarian that sacrifices HP for Temp HP, and in doing so, expands Rage to work with ranged attacks and spells.
Barbarian that has two special spell lists, one for combat spells and one for mobility buffs, that the barbarian can choose 1 from each of to cast when he begins his rage, and they stick until the Rage ends.
Barbarian that has a Ranger spell list and can temporarily remove Rage to cast a spell, and has several abilities that activate when doing so (like Dodge).