Can the PDF invoice contain the Online payment URL?

I would like to add the online payment URL (that I send out in the invoice email) to the actual invoice PDF that is created.

I have look at the the invoice templates and when I edit a template I do not have the place holder for %OnlinePaymentURL%

I assume if add it manually it will not work? and if not can I request this be added? It seems like a simple one that could be included without much effort.

Cheers

Dave