I’m not a programmer, so I will just throw this out as a question.
Could not the BPAY graphic be converted to a png image with the white background set to be clear? At the same time, the Biller Code can be added. Even I can do that using Irfanview.
Then a Custom Field with no label can be created for Sales Invoices allowing the input of the Ref number.
The tricky part would be the HTML coding to align the two objects. That is beyond my abilities.
Two work-arounds: Insert the Biller Code into the image and for the Ref insert “See above”. Label the Custom Field “Your Ref: number:”, and have it appear just above the BPAY box. HTML coding and alignment problems are avoided.
Or, convert the image to a png and place it in a Word document. (Getting the alignment correct in Word is not difficult.) Print the Invoice from Manager, and then run it through the printer a second time to add the BPAY logo and information from the Word document.