They can be fished fine w/o bait. But I often use a very thick wrap on my kwikfish for one specific reason, the bigger / thicker the wrap, the slower the wobble of the plug ... and slower is often better when it comes to kings.

Because of this, you might try placing one of the Pro-Cure scent pads on the belly even if you don't run scent with it, or sponge pieces as has been suggested, both will help slow the wobble.

As to the type of fish, yes, sardine seems to work best, but herring and anchovy are other options as well. Never tried the cut-bait method with other fish types, but ????