print organizer using named expression

Doee anyone know if there is a way to specify a named expression that can be used to add an increment value string to the Name field of the Print Organizer (PO) list? For instance, if a file is added to PO that has 5 different areas meeting the print criteria so that it show up with 5 print areas, I'd like the Name values to show the design file name_01 through _05. At this point the only incrementing I can see is to add a sheet number. This works for the first file I add, but for subsequent files added, their sheet numbers wouldn't start with _01. Can a named expression be defined to do this?

 

Thanks,

Stephanie