One way to keep from overusing youngsters, but still giving them a chance to get an extended major league trial, might be to piggyback them, like sometimes happens in the minors. For example, they could piggyback Marshall and Guzman (maybe give them each four innings each outing) for one rotation spot and piggyback Hill and Marmol for another spot. You'd have a rotation of Zambrano, Prior, Maddux, Marshall/Guzman, and Hill/Marmol.