from what i have understood from here on BYC hens go broody as a hormonial (spelling?) deal. you cant make them go broody buy simply leaving eggs or anything, it may help some but doesnt exactly encourage it. this is what i have understood...may be wrong may be right but my 2 cents.
If you leave a few eggs(real or artificial) in the nest it may encourage her. If she does take the nest, after her setting a couple days, go to her in the dark and replace the dummy eggs with ones you want her to hatch.......Pop
In responce to Kyle`s post, I have encouraged some of my Asil hens in the past by merely leaving 2 eggs in the nest. Asils are notoriously good broodies. After only laying 3-5 eggs an Asil can be talked into setting in this manner......Pop