if you make a zoneOCR field that's multi-value and expecting multiple lines, you can use a function on the token to remove the "Invoice" line and empty lines, and then output that to a metadata field. Or manipulate the token however you like. 

This was something shown in a Quick Fields Training/Learning session at Empower 14. Joseph King taught a wonderful class that is a textbook example of what you are wanting to do with that sample. 

Good Luck with your session building, maybe you can get Laserfiche to provide you some of the documentation from that course to help in your work.