Display promo codes on customer record?

I have a promotion with single use codes where each code is associated with a particular customer using the 'recipient' field. I would like to display the promo codes associated with a customer account under the marketing tab on the customer record. That would give us one place to view which promos have been offered to the customer, and whether or not they have used them. I have tried creating a custom field, type list/record, and I see Promotion Code as an option, however I do not see a source for Promotion or anything else that makes sense.