Nerve Pain Numbing Agent?

Where my ultra running really gets unpleasant is some nerve pain in the bottom of my left foot, near the forefoot. Once that starts barking, it definitely makes things a beast. I've moved to about as cushy a shoe I can find, which certainly helps. But if there were something that would numb it just a bit, just to take the edge off, I'd be a much happier camper.

Anyone try or use anything along those lines that they recommend?