Even though I'm necroing (two months), I think that if a valid and easy to implement way to make this work a little better is proposed while Zanzarino is working on 1.4, he may as well implement it (MAY, mind you).
Said that, the easiest and surest way to do that would probably be:
Insert Redeem code (no check whether it is correct or not), choose your Nymph/Mark, validate it (now the game checks whether the code exists and it is unused, if both the conditions are fulfilled, you get your card).
I don't see any way to exploit this, aside from obvious hacking which could hit everything, really.