Another way would be to set up a "sale Item" that you insert couple of lines down in the Invoice I have many various no value sale items for various reasons from "happy birthday", "Closed for vacation from X to X" " Import and export data and information some countries require" etc. too my catch all sale item called "type info here" so when your processing Invoice just type in "item" column -
type info here t
ab to description column back space and insert what ever you want.