Import JSON feed data automatically without FeedMe
The answer is Routing.
Define a wildcard route
e.g. URL/path/*
Then tell it to use a particular template if that route is used.

The key thing to do (which I didn't do first time around) is:
Don't duplicate the same route in a section.
If you do, Craft follows the section path not the routing path and expect entries to be in the CMS.