Advise your users to go to Settings > phone updates and then uncheck the box for "Automatically download"
Then they get a notice that there is an update waiting and they can tap "get details" to see what the update contains before install.
I would assume that only OEMs and carriers (where applicable) get advance notification of updates.
As this is a fan based site in no way run by Microsoft, we only know when they hit - not before.