Check printing is a different scenario in Oracle, since the concurrent program is launched as a part of the payment process.
If the concurrent program is submitted manually then we could have manipulated it by wrapping in a different program and then calling two different concurrent programs having its output from two different trays, but in check printing scenario we don't have a work around.
By modifying the seeded code you should be able to achieve this: [Non recommended solution]
1. Create a wrapper program [call seeded check printing program (program 1) then a custom program (program 2), program 2 will print the non negotiable document ]
2. In the seeded code modify the concurrent program call to your wrapper program call.
NOTE: EVERY TIME WHEN A PATCH IS APPLIED TO AP OR IBY modules, care should be take to reflect the custom change.
Hope it helps, Thanks!
Please find some useful references in this regards:
How To Set The Printer Tray When Sending Concurrent Output To Printer [ID 740539.1]
How to Specify a Printer Paper Tray With Pasta [ID 241086.1]
How to Use Hewlett-Packard Printers with Multiple Paper Trays When Printing Requests. [ID 147712.1]
What are the Common PCL5 Printer Commands for HP Laser jet Printers [ID 135990.1]
How To Setup Custom Pasta A4 Print Styles And Drivers [ID 763274.1]