It may seem a bit odd, but my mother always made homemade chicken broth for our cats when they were sick and would not eat. If they would not drink the broth she used one of those syringes with-o a needle to squirt small amounts in their mouths. Once when our oldest cat was sick she and I made the trip to the vet every 2-3 hrs to go and feed him homemade broth with a syringe. He was at the univ vet school clinic because he got hurt several hours after the reg vet closed. I am sure canned broth (low sodium only, look for no msg or for the sodium content to not be sky high) is fine. Broth made from bouillon powder or cubes is not very healthy for them and may be way too salty and contribute to dehydration.
One other trick, if this cat likes to be clean/to groom himself, is to spread tuna juice (liquid from canned tuna) or chicken broth on his paws where he can lick easily.
Baby meat is very good for this kind of situation. Do NOT get the meat for older kids mixed with rice or vegetables or pasta or whatever. Get the little jars for the first feedings of meat. Cats don't need that other stuff and right now the protein is what they need.
Tuna can be hard on their system, so go easy with that at first. A bit of juice to get him interested and then a tiny amt. Or you can mix a bit of the tuna juice with chicken baby food if he on't touch the baby food.
I hoep some of this is helpful!