[desktop_multi_window] Is it possible to ensure that a subwindow cannot be opened while an instance of that subwindow is already running?

In my scenario, I've got a `PreferencesWindow` that opens as a subwindow via a keyboard shortcut. I've discovered that while that window is open, I am able to open more instances of that window via the shortcut. 

Is it possible to ensure that while a subwindow is open that no other instances of that window are created?