Calculating the Natgateway DataTransfer-Out costs down to instance or tag level

IHAC who have ec2 nodes tagged. When they send traffic out to the Internet from these nodes, they can see that traffic (DataTransfer-Out-Bytes) in the aggregate outbound reporting, but the traffic outbound to the Internet passes through a NAT gateway (for example, nat-XXXXXX). Passing through the NAT gateway, the tagging attribution is lost. Consequently, when they use cost explorer and filter on Tag and Usage type: DataTransfer-Out-Bytes, they get nothing. Is there a solution for this, so that they can correctly attribute data transfer out costs from natgateway by product or tag.