WordPress Set A Static Page/Template For All Sub-Pages

Okay so I have resolved this by combining several different wordpress functionalities:

  1. Catches the template include conditionally add_filter( 'template_include', '...' );, in my case based on a regex match of the expected URI pattern
  2. locate_template('example-template.php') to then resolve my (essentially) static template
  3. A query within my example-template.php that externally retrieves the resource
  4. This must handle 404s interally as the response will always assume the post can’t be found, I am always setting the header response (before get_header in the template to 202 where the resource is found.
  5. Example; if ($resource) { @header($_SERVER['SERVER_PROTOCOL'] . ' 202 Accepted', true, 202); }

Bit convoluted, but really not too much work for what I required.