Pulling information about TeamRaiser Discounts through Web Services

Is there any way to obtain information about discount codes used by Team Raiser registrants during the registration process?

TeamRaiserRegistration record has a DiscountType and Discount, but neither of them identifies a specific code used during the registration (one is a single letter, the other one is % of discount applied). In theory, there is Payment information in TeamRaiserRegistration as well, with Discount being a part of it. You can obtain a Total Amount and Discount IDs from there. Unfortunately, it can only be pulled if there was an actual payment during the registration process (an additional gift or discount lower than 100%). It seems like for full 100% discount codes, where payment amount is $0, the payment information, and together with it the discount ID used during the transaction, are not recorded. Querying by the Payment.Discount.DiscountIds also returns only the records with payments.

Any suggestions?