No...he can not tack on.
Believe me, this is not going to work out the way that you and others unfamiliar with government employee pension rules think. I have personal knowledge of similar situations. He most likely will not need go through the motions and work for 2 more days in another position; the swamp protects its own. By the time the lawyers are through bamboozling the pension board that will eventually decide this... being two days short will not mean squat. He will get his full pension and he will get the book deals and the lecture money and the whole shebang. It is ridiculous; I wish it were not this so, but it is.