I just mix their feed with warm water for the mash. Cold water in the summer, when they need a cool treat.
Another advantage to this is that it makes it easy to mix in things that they could use more of, like protein during molting. I know they'll eat the mash, so I add either calf manna or...
I second the warm mash made from their regular food. I feed my chickens that every afternoon, and they love it. They think it's a treat, but it doesn't dilute any of their nutrition.