In any case in which wages are paid by an employer without regard to any payroll period or other period, the withholding allowance allowable with respect to each payment of such wages shall be the allowance allowed for a miscellaneous payroll period containing a number of days equal to the number of days (including Sundays and holidays) which have elapsed since the date of the last payment of such wages by such employer during the calendar year, or the date of commencement of employment with such employer during such year, or January 1 of such year, whichever is the later.