Paypal and $0 total order


We have a client who offers coupons ( cart promotions ) for “order $24 or more and get $24 off” which most times leaves just the shipping to be paid for. Her current payment method is only Paypal but Paypal won’t process an order that has a total $0 - the shipping is passed separately and not part of the total order amount. Does anyone know a setting we’re missing in either cs-cart or paypal that will either pass the shipping as part of the order total, or one at Paypal that will accept orders that only have shipping attached?

Thanks so much for any help you can give us.