Content Listing and Content Blocks in UP

It seems in Standard User Portals that the Row ID of the COntent Listing that links the Content Listing to the Content Block and allows modification can only rely on one unique identifier. For instance on Sales Lines the line number is the unique identifier. I have a Time Sheet Mod I am trying to put on UP that has two unique identifiers on the Line level - that is work date and a line number. I need two identifiers so I can filter by the date and show different time periods. Has anyone done any work where they have managed to pass two variables as the ROW ID on the Content Listing to allow modifications of Contents?