As stated previously, this payment should be done twice yearly, before the primary and general elections.
Take the taxes out of their paycheck and accrue it in a local "checking" account [which can only be used for tax payments, federal, state and local] and force them to write out the check, sign it and mail it in.
This is my solution (since true tax reform is, for now, unrealistic) having done payroll taxes for years and seeing what small business pony up to the IRS. With direct deposit systems it would not be a complex thing to set up automatically.