How to stop exposing new entities to Alexa?

I am using Nabu Casa for Alexa integration and it works just fine. However I want to keep control over what is exposed to Alexa, to keep things tidy at the Amazon end, but every time I add a new device to HA, it is automatically exposed to Alexa (and Alexa sends me an app notification).
How can I stop this behaviour and only expose entities to Alexa manually using the Configuration > Home Assistant Cloud > Alexa > Manage Entities interface?

If you go to manage domains (top right in Home Assistant Cloud | Alexa | Manage Entities) and set all domains to “off” no new entity will be exposed to Alexa unless you specifically say so.

Ha. As easy as that! Thanks