Then you just pick an elemental type you can enchant a hammer to deal and go to town on buffing that elemental type (because most damage bonuses only trigger when *rolling* damage, which is why the three-attack power is supposedly balanced; but radiant damage, whoof:
Get yourself a hammer that doubles its damage bonus to the attack, grab a class feature that inflicts radiant vulnerable 10 for one round every time you hit with a radiant power (and you're attacking three times so one of them will probably hit), take a feat which gives you Con mod temp hp every time you hit for radiant damage.…