Labels for multiple credit cards in customer record

Labels for multiple credit cards in customer record

I am using books for selling good, services, and even subscriptions.  A customer may have more than one credit card present in their customer record.  I would like a way to identify the purpose of one card vs another. 

Use cases: 
1 card is present only for recurring subscription charges.  
Multiple buying centers:  One organization may have two organizations who buy.  It would be helpful to indentify the card associated with a particular buyer.

Ideally if we could have a comment field associated with a credit card record that is a zoho-only field it would be perfect.  This would allow for users better assigning the correct card based on the use-case.

But, assuming there is no quick fix the only work-around seems very unreliable.  ....add a comment in the customer record identifying the last four digits associated with a particular purpose/buying center.

Anyone have a better resolution for this problem?