> He is fed on a raw diet and is only having 2 % of his body weight,
Is that 2% of the weight he
should be or the weight he is? That may make the difference, food quantity only needs to fed a little too much at each meal to have a commulative effect of weight gain.
Can you just up the veg% of his food (cut out some meat & replace with veg).
Once he is at his ideal weight, you'll have to re-adjust his food again to maintain weight.
BUT I don't know anything about raw feeding, hopefully somebody who does may have some good tips for you.