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Firstly, you don't need CVV number to process a credit card. Using a CVV may lower your fees for card-not-present transactions but in many cases just not passing it to the provider will still result in a valid authorization.
There are some exceptions:
- The fraud filters in your merchant account REQUIRE a CVV
- The issuing bank has strict Card Not Present fraud monitoring in place which may trigger a decline
However, what I think your client (and possibly you based on context) may be missing here is that you never need to store the credit card number after an authorization has taken place. Most gateways allow you to capture the funds with the authorization key and your API token at a later time.
Because this key is not considered cardholder data by the PCI definition this can be safely stored without risk to the card holder.
So, what I would do, is develop the system for the authorization to take place on a live gateway at the time of the order placement and then be captured later on from another system. This will require some development but is most likely the safest approach here.
Lastly, there is no rule against storing credit cards themselves. You may not want to store them because the PCI burden is too great to bear for the size of the business, but it is not strictly prohibited to store the 15 or 16 digit PAN. If you do store card numbers there are rules to how they should be stored.
Review the latest PCI 3.1 documentation here:
Review some of my presentations on the topic of PCI compliance here:
Wow such PCI Compliance @ Meet Magento Spain 2015
Secure Commerce Panel @ Magento Imagine 2016
Read my blog on achieving PCI on Magento: