You can capitalize on his interest in karate and add a visual-spatial component by target practicing with him at home using focus mitts and kicking shields. As his ability to hit a fixed target improves, you can start moving the pads around thus enhancing the challenge.

http://www.amazon.com/Shock-Wave-Cu...fined&sr=8-1&keywords=focus+mitts+karate

http://www.amazon.com/Combat-Sports-SHIELD-5-Big/dp/B001WX5Z7C/ref=pd_bxgy_sg_img_y

Another indoor idea is to hang a light ball (tennis) from an adjustable string attached to the ceiling for a variety of activities - throwing, swinging, orbiting, batting, kicking, jumping to reach, etc.