You can set your Ethernet connection to be metered and tell Windows not to download over a metered connection, it requires a registry hack, but it's relatively straightforward.
Doesn't reliably stop updates any more - the description has changed to:
"Available updates will be downloaded and installed automatically, except over metered connections (where charges may apply).
In that case, we'll automatically download only those updates required to keep Windows running smoothly."
In my experience it now downloads upto ~70% of available updates (not sure if it is a bug or intended) since 1706 with a connection set to metered. Makes the ability to set a connection to metered a bit of a joke.