Credit for service as counsel of the Chicago Welfare Administration. Any person who shall have rendered service before 1941 as special corporation counsel of the Chicago Welfare Administration, for which service no credit has been granted in this fund or in any other public pension fund or retirement system in this State by whatever name called, may establish credit in this fund for all or as much as that person may desire of such service for a period not to exceed 50% of all of the service rendered by paying into the fund an employee contribution plus the employer contribution equal to the payments which would have been required if such service has been rendered as a participant in the fund, based on the rates of compensation in effect at the time the service was rendered, and rates of contributions that are in effect today with interest thereon at 4% per annum, compounded annually, from the date such service was rendered to the date of payment.