Linking Item No to Part Drawings

I am sure this has been asked many times, my customers want to have multiple parts on an A0 sheet, I have a block which is linked to two custom properties "Quantity" and "Item No".

These custom properties are in my Solidworks Bom (not excel bom) the columns are adjacent to the Solidworks generated "QTY" and "ITEM NO" after ordering the bom I then manually type the information from the adjacent column, i.e "ITEM NO" 1 to "Item No" 1 this inserts the custom property into the part and updates the block on the A0 sheet then hide the two columns on the BOM, no problems everything works ok, but there must be a way of linking the Solidworks system properties with the Custom property?

Everything I do is a one off including toolbox parts which are saved to a separate part number and then disabled from toolbox.

SolidworksBill Of Materials