If the VPS with public IP is the same doing the NAT to the storage pool then yes, you can use NAT to access the storage pool from the public (valid) ip addreess.
You can also create a vpn from the public IP VPS to the server doing the NAT to the storage pool and serve content from there.
In any case, all content served by the public IP address will be accounted for, there's no way to avoid that (so directly answering your question about VPS badwdith usage: no, there's no way to not use the VPS bandwidth to do that).