Jobs: Once invoice has reimbursed list invoice number against original transaction

When a Reimbursables are applied (added) to an Customer Invoice it would be great if the Purchase had the Invoice # applied to it.   We do this manually for every Purchase/Reimbursable.  We do this line by line (as sometimes we have different Job Codes per one Purhase Invoice).   

"INVOICE Number applied to PURCHASES automatically: Reimbursables"