I found a baby sparrow. Has most of his feathers. Feeding him Exact w/wet cat food. Won't open mouth. Help!?

There was no way to put this little guy back in the nest on the side of a building 30 feet up. He was on the hot pavement in a parking lot and it was 107 degrees. He was so dehydrated. He won't eat except for little bits that I put on the side of his beak. Can't get him to open his mouth. But I do see a little food in his crop. How often should I feed him and how can I get his mouth open? He made it through the night and chirps continuously. Thanks! Any ideas are welcome.