Any member who was formerly an employee of the Foundation for Public Broadcasting in Georgia, Inc., who became an employee of the Georgia Public Telecommunications Commission created July 1, 1990, by Chapter 13 of Title 20, and who became a member of this retirement system at that time shall be eligible to receive credit for previous employment service with the Foundation for Public Broadcasting in Georgia, Inc., upon payment to the retirement system of his or her accrued liability, as determined by the board of trustees. Such option must be exercised by such member not later than December 31, 1998. Any member electing such option may purchase all or any portion of his or her previous employment service with the Foundation for Public Broadcasting in Georgia, Inc., and full payment for the accrued liability of such service shall be made at the time of such election. Each such member shall be allowed one election and no additional service may subsequently be purchased.