Do what you gotta do to get his energy up / calories up so his cells can *FUNCTION*! That's number one. Water and sugar. Do what you gotta do. As soon as you can introduce more and more healthy food. Personally he sounds fussy so I would just go with juice boxes all day and introduce as much fruit as he will have slowly over time. Carbs make a sane mind. All vitamins and no carbs makes Jack a crazy mofo.
PS he's going to need heaps especially in the first weeks his body is going to suck up those carbs like nuts. Don't hold back.
Yeah it's part of the conditions of this site that you don't promote that here. I used to use it, but no longer need to after discovering this lifestyle. Our vitamin / mineral requirements are far different on a vegan diet than what they are on a SAD diet. SAD diet is what is used to determine most "requirements" of these things.
I disagree, if he's on 700 calories a day WTF is that!? I get from 2500 - 3500 a day and that's only cause I don't do much exercise just now. ANY less and I feel bad that day or the next day, and feel better soon as I eat more. Water is primary but also primary at this stage is easy calories. If you go on less than that you will get hospitalized and what will they do there but pump calories into you via intravenous glucose drip to keep you *alive*. Frankly if he has to drink sugar water to supply his brain and organs with the most basic macro nutrient = glucose, then that's going to be far better than nothing. If not sure, ask someone whose starving to death, and that's basically what he's doing. Carbing up by whatever means necessary at this stage will enable healing to take place which will mean he can start to eat again.
Why doesn't he just get onto some sugary organic juice boxes and just drink those all day long, that will help with hydration and calories in one go.