If you are allowing him to use your vehicle, he's covered under "permissive use", you don't need to add him. Plus, if you call to add him, they're going to want his Drivers License number so they can run his MVR, but he doesn't *have* an MVR, so there's a lot of ways this could go sideways.
Before you call, I'd suggest reading your policy, specifically under "Who Is An Insured" to see if that answers your question.
Source: I work in Property/Casualty insurance, 10+ years experience