Mail Merge Split into Seperate Documents

Mail merge from spreadsheet and split into separate word docs with filename based on a number of fields from the spreadsheet. Dialog box required to select excel spreadsheet to use a mailing list, user selects fields from the spreadsheet to name the separate working docs. I have attached a sample spreadsheet and the mail merge template. I would like the dialog box to be able to select up to 4 of the spreadsheet fields I.E Expiry Date - Client Code - Policy Number to be used to name each of the individual word filenames