I just take them off the nest several times a day (3 or 4) and kind of stomp or chase at them til they get on their feet and start moving around, eating, etc. They go back on, but so far it's stopped the broodiness for 3 or 4 of them in a few days. Wouldn't always work I'm sure; some are much more determined than others. It's a good idea to make them move and eat anyway, though. Supposedly they leave the nest once a day to eat, drink and poop. Trouble is, some never leave. This at least ensures they get some nourishment.
If no one is laying, though, removing or closing the nests would certainly be simpler. If they don't just make a nest on the coop floor, of course.
The most sure fire way to break them is give them a few fertile eggs so they will have babies to raise, or buy a few chicks and slip them under the broody (probably best done at night.)