So for xylitol, I have a friend who has been taking megadoses to cleanse. (It was recommended by his dentist as a way to clear up this low-lying infection that was persisting after he got his wisdoms removed.) It's generally used to prevent/treat staph/strep infections. Lots of people use it for kids' ear infections, and for nose/throat sprays.
I'd start him about 2 teaspoons every couple of hours. (Be aware that diarrhea can occur at high doses but is no big deal.) Just drink some tea and use the xylitol as a sweetener.
While the water's warm in the kettle, you can also mix some xylitol with some Sea Salt in the water and have him gargle with it, which will really help.
If it doesn't go away, I'll send you my Lidocaine!