Authorize.net and "Free" coupons

I currently have a client who would like to offer gift cards for some products in the store that would essentially be giving the end buyer the item for a $0.00 amount once the coupon has been applied. Her setup is currently using Authorize.net and still asks for a credit card even with a $0.00 cart subtotal upon checkout. This of course fails processing and the user cannot complete their checkout. Is there a suggested fix/way around this issue?