As long as he has the season pass voucher, he can process it by himself. He doesn't need the credit card that was used, but it would be a good idea if he had the confirmation number from your order in case there's an issue.
Panda Express and Chick Fil A aren't run by the park. IIRC, they don't even use the same register system.
Is this like the websites that are constantly in beta?
The website is in an earlier post in this thread...
Side note: Do you still earn points and get the extra FUNPerks receipt even if you haven't signed up online yet?