You could point out to him that if he loses his job on account of drinking, that he will no longer be able to afford to buy alcohol. The same goes in the case of the driving privileges, which will be gone if he gets caught DUI, or worse, if he hurts someone.
Tell him to look up the DUI penalties in your state online, and point out that anyone could potentially call it in. Alcohol is his top priority, and that might get his attention, even if only to protect the drinking.