Send Ctrl+Q to underlying app in Gnome Boxes

I’m running Windows 7 Pro under Gnome Boxes on a Librem 13 (which itself is still running PureOS). I’d like Ctrl+Q to be sent to the underlying Windows application, rather than closing the Gnome Boxes session.

I can disable Ctrl+Q easily enough, by clicking on the down arrow at the far right of the PureOS status bar at the top of the screen, then clicking the gear icon, then Keyboard, then + at the bottom of the hotkey screen to “Add Custom Shortcut,” and adding one as follows:

Name: CtrlQ
Command: [I’ve left this blank]
Shortuct: Ctrl+Q

But I don’t want to disable Ctrl+Q altogether; I want the command Ctrl+Q to be passed on to the underlying application. (For my purposes – running WordStar for DOS, which uses Ctrl-Q as a menu prefix, passing Shift+Ctrl+Q or Super+Ctrl+Q would work equally well, as WordStar recognizes these as the same as plain Ctrl+Q.)

Just typing Ctrl+Q in the “Command” field doesn’t do the trick.

Any suggestions gratefully received!

Many thanks!