Id honesty reccomend he remodel the change up.
Instead of just holding the ball deeper in the hand, try another grip. Here are some:
I'd reccomend he play around with variations of these. I'd also say to try pronation to spin the ball on the side if he's comfortable with it.
As for the 2 seam, to get more movement he has three different options here.
1) play around with the grip some more till he finds one that works
2) try adding finger pressure
- middle finger pressure is for sink
- pointer finger pressure is for arm side movement
3) try pronating the ball. The more of a tilted axis is spins on, the more movement it will have.