I briefly went into the franchise mode. I noticed that the star players that was put in Single A are on the big clubs. Which is cool with me. This game doesnt allow you to put players on the disabled list, unless it happens while playing Franchise or Season.
Also Harper has that kind of potential. I remembered last year in the Show 11'. Harper got traded to the Twins. He was the CPU Twins starting RF. I think he hit for .280 with 25HRs. So what you should probably be doing; is trying to get him on your team.