Exactly... all you'd need to do is download it to PDF and edit it in Acrobat then print that. I don't see this as really much different since it doesn't involve hacking into the airline system and giving yourself a reservation.

With Passbook, you could screenshot the Passbook generated boarding pass, edit the image in Photoshop and then just pull up the image instead of a true Passbook boarding pass.

But I have to imagine in either case that whatever you produce won't "scan" correctly in the airline system.

If you did your homework and assigned yourself an empty seat in J/F, you could theoretically board the plane, show them your "boarding pass" and take the unoccupied seat. You still wouldn't be on the manifest as a J pax, though, so you'd have to get a FA willing to chalk it up to computer error and not really look into the matter any further. A lot of risk there...

**EDIT** One thing you could do pretty easily and get away with pretty easily is to print a separate boarding pass for yourself in J with the sole purpose of accessing the premium security line. I've never seen them scan BPs, so I think this would be pretty easy to get away with with a near-zero chance of being caught.