Short of spraying cold water on his face in the morning...ummm, he's gonna have a wakeup call when his boss fires him for being late reporting for his job? And how will that look on his job record?
It's a good thing that your son has chosen to take a "tolerance break" from weed, but the withdrawal symptoms can kick in some days/weeks later, if he doesn't recognize them for what they are. Hopefully the break is long enough for him to recognize the problems that weed usage presents and maintain abstinence long enough to learn about and assert some mastery over his own issues, whatever they may be.