I import customer invoices as bulk. (the data i generate out of amazon reports )

I need to store additional text info for each invoice, not only the usual fields like invoice number, product id, product name. 

I.e. i want to store the Amazon Order ID, if it was FBA or FBM, Shipped from & Shipped to country. Also the download link for the amazon generated invoice. These data is not for former processing, only for manual control.

Which fields can i use for such text while importing? On the GUI there is a field for notes, which i could use. But i have found no way, to fill these note field, while bulk import invoices.