I had to put my kitten down today because of fading kitten syndrome... then later found out that even if she is completely limp and lifeless... rubbing sugar water on her lips may get her to drink and recover.
Sorry to hear that, mate. Chin up. Get yourself another kitten, maybe two. Also, what you said your kitten had can be caused by a myriad of issues, and I'm sure the vet would have mentioned this "treatment" were it feasible. Don't stress it man, you probably did the right thing.