(i) An individual who is employed on a full-time basis as an officer or employee of a statewide teacher organization that serves System participants or an officer of a national teacher organization that serves System participants may participate in the System and shall be deemed an employee, provided that (1) the individual has previously earned creditable service under this Article, (2) the individual files with the System an irrevocable election to become a participant before January 5, 2012 (the effective date of Public Act 97-651) , (3) the individual does not receive credit for that employment under any other Article of this Code, and (4) the individual first became a full-time employee of the teacher organization and becomes a participant before January 5, 2012 (the effective date of Public Act 97-651) . An employee under this subsection (i) is responsible for paying to the System both (A) employee contributions based on the actual compensation received for service with the teacher organization and (B) employer contributions equal to the normal costs (as defined in Section 15-155) resulting from that service; all or any part of these contributions may be paid on the employee's behalf or picked up for tax purposes (if authorized under federal law) by the teacher organization. A person who is an employee as defined in this subsection (i) may establish service credit for similar employment prior to becoming an employee under this subsection by paying to the System for that employment the contributions specified in this subsection, plus interest at the effective rate from the date of service to the date of payment. However, credit shall not be granted under this subsection for any such prior employment for which the applicant received credit under any other provision of this Code, or during which the applicant was on a leave of absence under Section 15-113.2.