I mean I hear what you are saying, but they are either going to sign a RHB who isn't good enough to play regularly against RHP (which means Marsh is primary LF and Rojas is CF) or they are (which means Marsh is primary CF).
They can't put off that decision until Clearwater, and what's more, I don't see what Rojas could really do in spring training to change anything. He could put up a 1200 OPS and it won't mean anything more than what Cave, Sosa and Hall did last year.
No matter what he does (or shows the coaches privately) it's still going to be pretty much the same situation that already exists, that A) he's good enough to play in MLB now if they want, even w/ a light bat and B) it couldn't hurt if he spent more time in the minors.