If you are that consequent with the presuppositionlessly nature of the Dark Urge, a dip into Cleric (Tempest or what else) for me would be out of the way too, as you depend solely on the grace of a god. Only a pure Sorcerer would then fit.
I never saw the Barbarian Rage as a special preparation. It's just the inner wrath that comes out at will, you need to click a button only because of how a game works. So I would not exclude a Barbarian from the perfect Urge class.
