How can I add variant barcode number to a packing slip without apps?

Does anyone know how you can add the variant barcode number (not the image) to the native Shopify packing slip?

I don’t want to use any apps and I have spoken to Shopify Support who can only put the suggestion forward to the developers. I know there is this variable:

line.variant.barcode

but Shopify are saying it still needs advanced coding to add the barcode number to the packing slip.

Any help and further clarification would be greatly appreciated

Many thanks!