Merge field for notes/comments from the donor to the tribute notificant

Some tribute donors include a personal note to be shared with the notificant. We would like a way to automate adding these to the Tribute Letter. The easiest way to do that would be if we had the ability to select the Transaction Note field to be included following the donor's address block. We can't use a custom data field because those are per constituent, not unique to the transaction. If the constituent made multiple tribute gifts those notes would be mixed up. Can you add this to the data selection options for tribute letters?