After a bit of searching, I found what seems like a simple solution.
When TRON 2.0 is running, press the Windows key and P key simultaneously. The game window should minimize, and a popup appears on-screen allowing you to select which display you want to use. You click on either "Projector only" (Windows 7) or "Second screen only" (Windows 10).
This should cause your second screen to still show the minimized game on the desktop, and your laptop screen should have gone dark. Now click the minimized game window in the Taskbar, to restore it to fullscreen. After you're finished playing the game, hit the Windows key and P key again, and select "Computer only" (Windows 7) or "PC Screen only" (Windows 10). Your external monitor should go dark, and the laptop screen should be active again. Then Windows + P and "Duplicate", if you want, so both screens are active.
