The only workaround at the moment would be to leave a Wyze Plug plugged into the wall doing nothing. Then you could trigger that plug to turn on when the door has been left open, and trigger Alexa to say something when the plug turns on, then turn the plug off.
I’m hoping Wyze will add a virtual switch function soon. That would streamline the process and wouldn’t require you to use plug hardware for a software-only purpose. You can vote for that here if you’d like to see it too