A State may elect to offer a premium assistance subsidy (as defined in subsection (c)) for qualified employer-sponsored coverage (as defined in subsection (b)) to all individuals who are entitled to medical assistance under this subchapter (and, in the case of an individual under age 19, to the parent of such an individual) who have access to such coverage if the State meets the requirements of this section and the offering of such a subsidy is cost-effective, as defined for purposes of section 1397ee(c)(3)(A) of this title.