Not sure if I fully understand. I have a client with a similar scenario. At my client, they are hand adding the new customers and the associated credit cards, since they get so few new customers. Then the VI Import into Sales order assigns the default customer credit card automatically.
In Customer Maintenance, there is a field called ""Default Payment Type"" if that is set to Credit Card, and the customer has a ""default Credit Card"", then the Sales Order should automatically import with that credit card on the sales order.