The question is: would he catch it if the batter wasn't there? Chances are, he would.
He's likely anticipating the batter being hit by the pitch and is therefore is not getting his glove where it needs to be in order to catch the ball. His glove needs to be at the other end of the trajectory and has to assume the ball will not hit the batter. There is no other way!
I think someone stated earlier: set up a machine, get used to receiving the inside pitch and then have someone step in to distract him. Perhaps hang some paper (or something that won't deflect the ball too much) on the inside of the plate and have the machine throw through the paper. The ball should be caught even after hitting the paper. Of course it may be a pain to set up the paper over and over again but this has to be corrected.