I know its been almost a month since Get Some suggested the ole' rice in a bucket exercise, but here's how its done. Just take a 5 gallon bucket, fill it almost to the top with uncooked rice, and the apparatus is complete. Now just set it down in front of a chair and dig your hand to the bottom of the bucket, not by moving your arm back and forth, but by closing and opening your hand only while keeping a downward pressure. Not only should your fingers, hands, and forearms burn after just a few minutes, but you will develop callouses on your fingertips (which is an added benefit for pitchers JdJack).
You could superset this with a farmers walk, or just set it in front of your favorite chair at home and do it during every commercial. Or if you don't watch tv, at least you can do this at home. This does work.