I know for sure that Costco sells CPK gift cards at 20% off ($80 for 2 $50 gift cards). There's also sometimes a Sam Choy's or dk-affiliated restaurant gift card (e.g., dk steak house). I'd call the Iwilei Costco and check.
By the way, if you're looking to get good meal deals while on Oahu, you'd probably have a better bet with the Entertainment Book. A much larger variety of restaurants to choose from at a deeper discount (usually a 2 for 1 coupon).