Why not use shipping terms?
We created a Ship Via for this and then our shipping department knew to bill the customer account in Shipstation for example.
One thing to improve this would be to add a Customer Attribute for their account number and then call that to print on the shipping confirmation if that works for your flow. In our case we already have a shipping notes custom field.
To add that to the shipping confirmation report, you’d want to add the CSAnswers table to the schema, the relationship would be Noteid of the Customer and RefNoteID on CSAnswers, then create a hidden parameter with a default value of CUSSHIPACT (or what ever it is) so you can also add CUSTSHIP = ATTRIBUTEID in the relationship. Be sure to use a left join.
Thanks for the input. We do a lot of exporting and have detailed instructions and have not found a good place for this information. i like the idea of the Attribute