Paint numbers on baseballs and as you pitch them in he doesn swing, he simply yells out the number as soon as he can read it.
Get three different colored whiffle balls, say red white and blue. He stands ready to hit, with his eyes closed. You soft toss them to hit and when they are close you yell go and he opens his eyes and only hits the red one letting the white and blue ones go.
Play every game as if it were your last