If he is vomitting and refusing to eat, it is very possible that he has a blockage. The trouble with blockages is that they can cause septicemia when waste builds up in the system, and they can decrease circulation to parts of the intestines. He may require surgery, not to scare you too much.
My advice would be to listen to what your vet says; if you keep him well hydrated, it will "water down" any waste levels that could be growing high in his blood. The advantage of pedialyte is that it also keeps vital elecrolytes and water soluable vitamins he is losing from vomitting in his system.
The vasaline I am assuming is to help lubricate his bowels in case there is a blockage? I would guess that if they make anti-hairball pastes for ferrets, this could help too, but if your vet didn't suggest it, it may not be the best idea.
That aside? Just keep him warm and comfortable; he is allready ill, and stress would only make it worse. I'm surprised you don't have an emergency clinic in your area; they are usually open night and day, including holidays. But, it looks like your appointment is as soon as you can get it, so until then, I'll have my fingers crossed for you.
Just as a side note - please in the future only let your fella loose in "ferret proofed" rooms; most of the ferrets we see in practice are there because they ingested something harmful. If he has so much roam that you can't even find him sometimes, that is a bad thing; the room he is in shouldn't have any unsafe toys, electrical chords, small injestible non-food items, harmful foods, open toilet bowls, garbage cans, etc. It may seem more restricted and less fun, but trust me - you'll be happy for the load of stress it will take off of your shoulders.