The Virginia Retirement System may enter into an agreement with any political subdivision of the Commonwealth to permit participation by the political subdivision’s employees in the cash match plan established and administered by the Board pursuant to § 51.1-607, except that political subdivisions of the Commonwealth otherwise participating in the retirement system pursuant to Article 5 (§ 51.1-130 et seq.) of Chapter 1 shall participate in the cash match plan established and administered by the Board pursuant to § 51.1-608 to the extent necessary to provide benefits under the hybrid retirement program described in § 51.1-169.