sorry, but it is up too the hen...if she sees a pile of eggs in the nest and she wants to hatch them she will or she will just go about her business and ignore them all together....Incubators are cheap and fun...get one and enjoy watching your eggs turn into chicks right before your eyes....but get a good one with a fan and an egg turner, hovabator is a great choice and a great price. Just my 2 cents.
How to make a hen go broody....oh my, thats pretty much up to the hen. The best thing i can think of....is Lights lights and more lights on your hens...but that coulld also cause other issues. Otherwise if you dont want to rely on mother nature , your best bet is to get an incubator. Little Giants are pretty cheap. Winter months, birds generally are not sapposed to get broody.