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Perfect.

At first I thought that this was going to be an impossible thing to do. My wife thought something was wrong with me. (Not sure if that has changed.)
Looking back, the biggest thing that held me back was my mind. And the fact that not many people can drive a nail through a piece of wood with their bare hand. I think anyone can do it if they believe they can. More than the little engine that could, you have to know you can. So, to help the mind out I think conditioning is the beginning of your quest to be a human hammer.
I started slapping an anvil. Sounds cool, anvil slapping. You can use any hard surface - stone, brick, wood; something to toughen the area where you'll be holding the nail. Start with soft slow slaps in the beginning and gradually build up to harder more forceful slaps. This will get your hand and mind ready for the impact of the nail drive.
Another area I noticed that was more sensitive was between the ring and middle finger where the nail protrudes. This area needed the most desensitizing. What you can do is put the nail in your palm, head of nail against the callous part of your palm, make a tight fist around the nail with the nail protruding perpendicular from your palm. See picture. Then similar to slapping, start tapping on a surface over and over to condition the inside of those fingers. Ideally the nail is driven in perfectly straight which will lessen the impact on the inside of the fingers. Now after your conditioning you will be ready to start driving.