TJ,
I agree with msscamp. Once your bull gets foot rot, he will go through an infertile stage. Not exactly what you want in a bull. I would call in a vet. The normal treatment for footrot is a course of antibiotics.
If you must do the doctoring yourself, I would say find a way to constrain him, give him a strong dose of LA200, or similar, and keep him in a small pen if available. If he doesn't start improving in 3 to 4 days, you will definitely need professional help. But, I would skip it and go to the vet. While the vet looks at him, you might want to ask him if he needs a semen test and when. You would hate to lose a calf crop to this...