We tried that sticking another hens eggs under our broody silkie. Somebody ate her eggs when she got off the nest one day, and she was just sitting on air. We took her off the nest and confined her for a couple days; then decided, what the heck, let's stick some other eggs in her nest, see if...
That's the only way we have ever done it. It is easiest, and we have found that mama hen in most cases knows which eggs are good, which bad, and everything else associated with incubating. And when they hatch, she keeps em warm, tells em what to do, protects em, and shows them a lot of things...