Plug-in To Capture Data While Submitting PayPal Payment

Hi all,
I have already spoken with PayPal about this and they don’t have a plug-in idea to assist, so I’m asking the true brains out there and would appreciate help with the following issue:
I’ve have a site that is basically a one-page where I offer a service to help medical offices convert old codes to new codes.
They need to submit their old codes to me by pasting them in a “box”, which would be sent to me upon clicking to pay via PayPal. PayPal has such an “empty” box that could be used for that, but it is extremely limited with how much can be entered.
My prospective customers could have hundreds of codes that could be up to 5 digits long each and must be separated by a comma or space.
Any ideas of how I can accomplish this? The list can’t be sent to me as a separate deal because there may be too many and they could get jumbled and not linked properly to those that have paid. That’s why I’m looking for a way to capture the data and the payment (and the customer’s return email address to mail the new list to)at the same time. I have to stick with PayPal also as I have no other payment setup ability.
Thanks for any and all help/advice.
Art