Keep training passing and I would start training either some OD or JS. Centers with amazing primaries, bad secondaries, and high salaries are a dime a dozen on the transfer market so if you want a more valuable and useful player, make sure that you train his secondaries. You're doing a great training this player so far so keep up the good work.
PS: If you want to train JS, train it with one on one guards. It gives you almost as much JS for a tall player as jump shot training and you'll get a lot of extra HA and DR.