get a stressball (not too squishy and not too... huhuh.. stiff) and use both your whole hand to repeatedly squeeze, and then several reps per finger. do both hands so that one is not overly stronger than the other. I do this at work a lot... not to mention typing seems to help with guitar fingering, and vice versa
do a "1234" motion with your fingers on your thumb and then "4321" like you are doing a chromatic lick
also, in order to strengthen your pinky you might just do finger lifts until you feel the burn, then rest.
doing these things especially when you must go a few days without practicing is highly critical, lest you lose muscle mass and density in your hands, which makes for sloppy playing the next time you pick up your axe.
but do be careful, you may develop a figity habbit or carpal tunnel if you overdo it