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.
With extended displays that should work, but I’m not entirely sure how practical it would be.
You have to be aware that you might face all the potential annoyances that you might encounter when regularly adding/removing any other (actual) extension display. E.g. apps that remember their window positions without doing sanity checks might end up being displayed at positions outside of your actual monitor – even after disabling the virtual one!
Better just use the virtual monitor as intended. It’s supposed to improve things and make them easier at the same time. The simplifying part gets lost when using it as extension display.