Aaron- Power = work/time... so literally you would need to figure out how to get bat through zone quicker.... IMO that would be figuring out how to get your body in the "torque" position ((maximum stretch).. .and then repeat it over and over until it is very efficient... then learn how to do it in game situations where you need to make "on the fly adjustments."
As far as workouts (gym) go... total body fitness, and make sure for core work, that besides "bridging" exercisies, that you do a number of rotational as well...
Finding someone in your area that might be a member of National Strength and Conditioning Assoc. (NSCA) would be a huge benefit...
but, JMO..