The total amount that may be so paid to or on behalf of an eligible student through this program shall not exceed the credit which would (but for subparagraph (B)) be allowable under this section if subsection (d) were applied by using the taxpayer’s modified adjusted gross income for the preceding taxable year. (B) Credit reduced by pilot program payments The credit allowable under this section (without regard to this subparagraph) for any taxable year shall be reduced (but not below zero) by the payments made with respect to a student under subparagraph (A) for expenses which would otherwise be taken into account in determining the credit under this section for such year. (C) Program participation Participation in the program established under this paragraph shall be voluntary with respect to both students and educational institutions