If you do give it to him, it will probably only be for a short time . . . I'd say that you will see him gain some weight on it.

When we got Brodie, Josie was eating kitten food and she gained several pounds

Kitten food has a lot more calories . . . you'll most definitely see an increase in his weight . . . but if that's not a problem, I'd give it a try!

Anything to get a finicky cat to eat!!!