Honestly... At this point I dont have much hope for the guy.
Big tank right now won't help, the guy can't probably move or if he can just barely.

id start with full on hydrotherapy, electrolytes 1:1 with dechlor water every day for 2 weeks, to help flush toxins. if eating - nightcrawlers coated with reptiboost for a week, qt tank. Feeding very small amounts, no more then small earthworm/nightcrawler at a time. And see the progress, review in a week.