It's a lovely idea but I'm afraid you overestimate the intelligence of some web users. I used to work for a company that provided the Credit Card processing for other companies. And one of the big problems we had was with users pressing the submit button more than once. Yes even with something as important as their own money they would ignore explicit instructions to be patient and not submit their credit card multiple times. I kind of felt we should treat it as a idiot tax but we had to protect the customers from themselves :-)

---If it doesn't fit use a bigger hammer