It isn't "beyond hope" but if you are an inexperienced leopard gecko keeper it might be a bit difficult. Have you kept leos before? To fatten him up, waxworms are great for that but provide very little nutrients, but you can give him a couple of those a week. You can go out and get some baby food like chicken or something and mix it with a bit of calcium and put a couple drops on his nose for him to lick up. that always seemed to work for me to get thin babies up to par with the rest. What's your set up like? you should have a warm side and a cool side. hides on each side and a humid hide on the warm side(at least thats where I prefer to put mine) if you can post a pic of his enclosure that would be great