If you go to SteamVR and select 'display mirror', you can then in the menu choose 'exit compositor'. You can then manually start the compositor again (C:\Program Files (x86)\Steam\steamapps\common\SteamVR\bin\win64\vrcompositor.exe) and then you can give it some command line parameters:
--keepalive (if you don't select this it will quit after a few secs)
I haven't really figured out what they are but maybe they're useful to your developers. What I personally use this for is that I kill the vrcompositor and then launch it from my debugger, so I can catch the initialisation part.
I thought I'd share it here, maybe it's useful to you guys.