There is an option in the config app that let’s you enable the virtual monitor manually from the vorpX tray icon. That way you can treat it as (invisible) normal second display.
BIG HUGE CAVEAT:
Windows restricts resolutions when mirroring displays to the resolutions supported by the less capable one, which obviously largely defeats the purpose of the virtual monitor. What you would have to do instead is extending displays and then use the Oculus/SteamVR mirror window on the actual monitor.
Since the virtual monitor is meant to simplify things, not making them more complicated, that’s not the default behavior, but with a bit of tinkering you *might* be able to make it do what you have in mind too.