[apowell]

If it isn't too late to select a payment gateway that supports a secure vault, perhaps Recurly.com would fit your needs? Personally, I don't know of any services that provide only the vault without the gateway or billing logic attached.

Plus, if a service had an API to transmit customer credit card data to your server so you could forward it to the payment gateway for processing, I don't see how that adds much security over encrypting and storing them on your own server (yes, I know this is a bad idea). A malicious individual with access to your server could still compromise your customer data.