Art,
What is the native application the print stream is coming from? There are multiple solutions out there that can do this but some of it depends on the native application. Maybe more information could help.
Also, what type of demo are they looking for? A log file output or just an automated system where they type or hit print and the command is sent automatically outputting duplex? There isn't much going on there just forcing duplex so I am curious what they are hoping to see.
All the best