Correct. The only way to return a payment, is by making a new transaction. If you, as a payment processor, want to be able to handle chargebacks, you'll have to hold on to the coins until chargebacks are no longer allowed.
Would it not be easier just to say that chargebacks are not possible, but the organisation will honour a valid claim by making a refund. Surely, the customer doesn't need to have the same coins returned, all he needs is to receive the equivalent in coins.