Hi
I had the same request for a check form in Canada. I solved it by writing the line item output into variables and print these variables in a second window. It was ~10 hours of effort, not a real nice technical solution but it worked.
If you require I can send you a PDF of the sap script form definition. You can contact me at jk_downunder@yahoo.com. Answers can take 1 week or more. 
Best regards
JD