That makes sense, here comes the dumb question: how would I set those session variables? And would those vars be available to me after I've completed the transaction with my payment gateway so I can present the user with a proper receipt? (I assume yes on the 2nd point but figured I'd ask anyway)
I also know I've said this before but I really appreciate the help, you're saving me hours on a project I underbid on in the first place. New lesson learned, don't give friends a professional discount ;-)