Add Reason to email sent to supplier at payment

Summary: We have been requested to investigate adding a payment reason (by invoice) to the payment email sent to the supplier when their invoices are paid.

Content (required): Our suppliers (this is limited to only certain sales/suppliers) have requested that we add information as to what they are being paid for on the email they receive when we pay them. Is there a way to do this out of the box (based on what I have read it doesn't look like it), it would appear to be a customization and if we have to customize what would be the best way to accomplish this?