Hi. I'm a combat medic and deal with dehydration pretty regularly. I'm NOT a doctor, and any advice I give is completely based upon my experience as an EMT and combat medic.
High creatinine levels indicate a problem with kidney function. Which can be caused by dehydration, and in this case probably is. As you've already stated that he is dehydrated, getting him properly hydrated should level him out.
So get him well hydrated. I suggest that you use watered down Poweraid or Gatorade. Not full strength. Put 2/3 cup of Gatorade into 2 cups of water and have him drink it. Do not use ice and do not chill it. Ice cold drinks require metabolic energy to process. He doesn't need to be expending that energy while getting hydrated. He should also not guzzle it.
As for your vacation, once he's hydrated, I don't think that having a couple of drinks will hurt him (2 or 3, no more), but he needs to ensure that he's drinking water and hydrating the whole time. 1 cup of water per drink. He'll know he's doing well when his urine is clear, not yellow or orange.
Don't worry too much, I'm pretty sure his abnormal levels are due to his dehydration. And getting rehydrated is pretty easy. Just be sure you slow down on the hydration once his urine is running clear...and just maintain that level with 6-8 glasses of water per day. If he begins to feel nauseaous while rehydrating, slow down.