The short version is that they only way the federales can collect a fine for not having health insurance is to take it out of your income tax refund. So if you set your payroll withholding tax to zero you won.t get a refund and you won't have to pay the fine. Of course if millions of people stop their payroll withholdings, the government will lose out on billions of dollars in interest free short term loans to use as operating money.
Details here:
http://www.forbes.com/sites/theapothecary/2013/08/28/white-house-publishes-final-regulations-for-obamacares-individual-mandate-seven-things-you-need-to-know/