Or you can buy a secure deposit credit card that has your name on it etc. I know a few out there that are really easy to get and it's a full credit card that has a very low credit limit. (Normally as big as you deposited).
So if you deposit 250.00 it's a 250.00 credit limit. You can then setup E-mail only billing and notifications. So all transactions will be hidden and you just tell the wife you use it for lunch, gas etc. Problem solved.