Triggers are based on either Session Events or Security Events, it is not possible to set them up by Session Group, but you could set up a trigger where if a machine with a specific IP address were to go offline by using the Session Event: Session.GuestNetworkAddress

Create a new session trigger - ConnectWise

This has been implemented as 'Require My Consent' here:
Enable a guest to require consent - ConnectWise
It enables a Guest to right click on the system tray icon to require consent, and in the case where a host is already connected, selecting the option will forcibly remove the Host from the sessions.