He needs a changeup. I would recommend trying both the circle change and three finger change. After a while, he can settle in on the one that works best for him. If you would like some info on these grips, let me know.
The key thing to the c/u is to keep all the mechanics identical to the fastball. No slowing the arm down, no dragging the foot. The grip alone will take off the proper amount of speed.
A freshman is old enough to learn the curve - if it is taught properly and he doesn't throw it much.