S2 member, like Telephone-card access

Hi!

I need to let an access to private page (with s2member) with a sort o code- voucher on a card (real, printed). Each card, of course, a different code.
My goal is:

  1. user buy a card with a code inside
  2. user go to website and use this code for n days of premium subscriber.

So i thought, i can insert myself random users (with level 1, with EOT of 3 days), and print the credentials on card/voucher, but EOT time starts (i think) when i create the user, not at his first access. So if i sell a card, for example after a month, for a user with EOT 3 days created a month ago, it cannot work.

Any idea?

Thanks!!!