Can I Force Feed someone?

You could place a beacon nearby that would give them a regeneration buff. Starvation causes a loss of 1 point every 4 seconds, while a level 1 regeneration buff gives 1 point every 25 ticks (or 1.25 seconds), so you should be able to keep them at full health even when their hunger bar is empty.

While you can't force feed someone, you could just change the setting to easy so that they can't starve to death, as @ZAD-Man said. You could have a dispenser with splash potions of health every few minutes as to prevent them from dying though. You could put cakes everywhere, but there is nothing that you can do to forcibly feed someone.