I would really think we should have the customer enter their zip code as a security and since we cant really verify that the real cardholder are the one who is using the card, most of the gas stations doing it ,why can we do it .
I usually stand with a first time customer and help them fill out their registration - telling them the benefits: you are rewarded a dollar; you can register your birthday; if you leave something in a washer or dryer, we an find your phone number and call you about it. So they always put in the zip code.
Problem is most customers all live in the same Zip code. How about using the street address ?