I don' think it is the wrong way to go. I will check your suggestion.
But I'm also open to other ideas
As far as i am aware there are no features in CEC that will allow you to 'exclude' or bar a valid HDMI device from the bus. HDCP obviously only allows devices on the bus with valid keys display certain content... but all devices you might want to connect will likely have valid keys I would imagine so I can't see there is any mileage in HDCP either.
Interesting requirement though!
All the best