is this possible?

I currently have a multisite setup with s2Member Pro and I wanted to know if this is possible. Basically, my goal is to allow users to purchase "credits" using s2Member. Right now, every user on my site has a user meta data of user_credits. Basically, I want to use s2Member to generate a one-time generic Paypal code/form to allow users to purchase more credits with any arbitrary amount. For instance, a user can purchase 100 credits for $10 or 50 credits for $5. I know there are hooks to capture when a payment is received so I can just update that user's credits from there.
Thanks!
Thanks!