Sales order line without item to purchase order

Is there no way to create a purchase order directly from a sales order line, if the line has a category only (no item)?

If one selects Purchase order directly from Sales order view, it show no lines to be selected. I think this is because they are in Sales category.

Adding the same category to a type procurement hierarchy does not make any difference.

Not a direct link, I believe it has to be an item because of how the system references and reserves the transactions. You would need to customise the system to achieve this.