Adding chicks to a broody hen?

I have done it several times with great success. Simply slide a chick under with one hand and then with the other remove the egg, repeat until no eggs/chicks are left. If you do this in the afternoon simply shut the hen and chicks up and leave them until the following morning.
Why do you think the other eggs aren't doing anything? Mum will normally be able to feel movement in the eggs and stay sitting on them until they hatch.