Ozone bagging would be great or soak in H202 footbath. (He may not be able to soak his feet because of the risk of infection. The skin may break down. However, he can do the ozone bagging.) He could apply the H202 topically.
Paste made out of olive leaf.
Castor oil pack
Grape seed oil
Cod liver oil internally. Diabetes interferes with your body's ability to fight infection.