If he wants to try, I think he should be given the chance. He should be allowed to show up to Spring Training and try to prove himself and if he is able to win a spot, fantastic. If he's able to stretch out and be a 6th starter, jumping up and down from St Paul, awesome. If he fails and just goes into the BP, that's fine too.
Refusing to allow a good pitcher to try to be better is just bad management.
SP can always fail and go back to the BP, but the reverse can really only happen once a year.