I once used that same logic hoping that Adams would indeed relieve for me in games 1 & 2 of the Semis (rested, too) if I waited until game 4 or 5 to start him. He never came in.
The reason I wouldn't have done it in your case is, even had Adams come in to win the game in relief, he'd be fatigued the next day, as far as I know. In my situation I was hoping he'd pitch games 1-2 and then come back with a day off to start game 4.
I think this is why in the 2006 version TSN is eliminating the SP designation for pitchers who were really primarily relievers, because SP/RP just don't get the bullpen innings they should.