Mail merge with personalized attachments

[sharke]

Does anyone know of a way to perform a mail merge whilst attaching a different file to each recipient? Probably through a 3rd party app or plugin? The only one I've found requires me to paste the full directory path to each file in a spreadsheet of recipients. This is too time consuming. What I need is the facility to prepare the mail merge, then use a file picker to select the file for each recipient. It seems like really simple, obvious functionality and yet I have been unable to find one single solution or near-solution online.