We're currently using all 13 scholarships, so there isn't one available for Manny to get here early even if he could graduate.
Also, it's not really a good idea for a 4-year player to do that. If he showed up for the spring semester, then this year would count as a year of his 5 to play 4. Your 5-year clock starts from when you enroll, not from when you first play, or practice, or any of that. He would be left with 4 years to play his 4, which would essentially mean that he wouldn't have a redshirt year available if he got injured in his career (or if he wanted to transfer). It made sense for DSJ because there was less than zero chance of him using his 5 years, but he was one of the few.