You're right, he'll need to have his own login to Wikitree - living people who aren't members aren't visible to anyone except for their profile manager.
Send him an invite by adding his email, as Steven Harris has said, and then, with him still logged in, go into the privacy tab on his profile and set yourself as profile manager so people know to contact you rather than him. He'll also need to be set to have a public family tree or his DNA won't copy out to anyone else.
Go into My Wikitree > Settings and turn off the daily and weekly emails, unless he's interested in reading them.
If his DNA test appears under the 'DNA Tested' heading on his profile, it should copy out to his family members in the next 24 hours.
If you added the test for him ages ago and he's got the DNA Tested badge but the actual test isn't showing up, you'll need to add the test again. A lot of test info on living people has been deleted for privacy reasons (people had been adding test details without asking permission).