For roots I imagine he could do a pretty good Vaseline barrier just by feel. Ditto for a touch up brush. If he was doing it at St Agnes (with no one to help him) he might time the growth of his hair or just wait for snarky comments about his roots, then do a full redye to make sure he doesn't miss anything. (I have no idea what frequent applications of shit-tier dye would do to his hair, though)
In college, Foggy could help him. Maybe have a heart to heart and help him consider if he even wants to do it anymore.

As for pubes, probably a scissors and comb-barrier trim to keep it orderly without too much risk of cutting his junk, or just fucking waxing it off bc why the hell not, he already does his chest