Wow.. The best thing you can do for him right now is keep it very clean and allow it to heal up on its own as much as possible. That's going to be a serious scar but I think s/he should be fine eventually. It'll take a few sheds but it'll be looking much better soon. I'm no expert, but the advice given on much smaller meal items to reduce the stress on the injury sounds just about right to me. Hopefully others can input here.
Good luck and please do keep us updated as s/he progresses! This will be one I'd love to see healed.