I believe they've done that a few times in their contention years in the 2000s with Liriano, Santana and Perkins. I think that was the plan with Garza as well but an injury got him into the rotation after one bullpen appearance, IIRC. They should have done it with Meyer - Gardy asked - but they didn't. Bluntly, after 2010 or so, they haven't really had great pitching prospects to try it with. They could've made Romero start in the pen this year, for example, but they let him start instead. And, obviously, they could have drafted Wright or another college pitcher (Dakota Hudson) instead of Kiriloff and Lewis.