It would be nice to have the feet toughened up to the point that you can get along without footwear on certain occasions. I see several web sites devoted to barefoot hiking etc. and even a product to toughen the feet http://tuffoot.com/
where one of the main ingredients is Balsam pitch. Other substances which supposedly toughen the feet are tannic acid, tea, witch hazel, salt water, alcohol and even urine. I am afraid that the only thing that will really work is time and pain and probably more than I would care to put into it.