I never used a fake egg, and mine chose the nesting boxes just fine, but at about 17 weeks of age, I keep them locked in the coop and attached run for about half of the day, letting them out when I get home after work, at 5pm.
That way, they're done laying by the time I get home, so they don't find a secret hiding place to stash a nest outside, where I can't find it.
Our chickens are free ranged but locked in a coop at night. We place a fake egg into a few of our nesting boxes roughly a week before or around the time they should be beginning to lay eggs. We have never had problems with them not finding these.