If the snake is vomiting and listless, I'd be getting it to the vet asap, not waiting a few hours. Not sure what kind of vet it is, but any animal that is vomiting and listless, usually is told to come in right away.

Sounds like you care enough about the snake, I'd be taking control over it. If your friend can't give it what it needs, make him understand that it's the best option.

Good luck and keep us posted