Like Kirbee said he can't apply till after the seaodsn, but he can try and make an appeal for a Medical Redshirt; however, those are usually kinda hard to get (over 3 games played), but it does happen, ala Daniel Cobb (not exactly the same, but close).
Beeware, why are you being hard-headed. Do you actually think there is any reason Sampson would get a MEDICAL REDSHIRT? Why would you ask such a question except to be a smart-a$$. O'Brien thought he was the second best running back on the team, and with Clinkscale hurt for UNC game he made the decision of using Sampson over the Walk-on Daniels. Down to 3 RB's, you're going to take drastic measures. Can you get over that?