He is not constituionally ineligible to the office of President. He is constituionally inelibile to be elected to the office of President.
The Amendment is fairly clear. 9 years,355 Days MAX.
The Only Real Argument that Could be made to put X42 NEAR the WH. Would be if Kerry needed to Replace his Veep, 2 years and one Day into his term.But he would still be ineligible for Re-Election in that position.
Personally I wish it weren't so, Because I would love to see Dick Cheney eat Clintons Lunch on MTP, or In a Debate.