This is honestly one of the few really good and creative ideas I've seen here in a VERY long time.
I really don't mind sharing an audio hash with someone that already has my full banking information/history in there. Not only that, I would be EAGER to do it if that will increase the security of the current contract that I have with them, specially since they found a way to do it that it's not bothersome at all.
Substitute money for information, and I would love to do business with you.
"You are already paying me $20, so you might as well give me $100."