No agency shall provide for its employees any program of life or health insurance supplementary to that provided under sections 84-1601 to 84-1615, except as provided in sections 84-1601, 84-1607, and 84-1608. The provisions of this section shall not deny an employee the right to purchase through payroll deduction entirely at his own expense individual life and health insurance programs other than those provided under sections 84-1601 to 84-1615.