How to hijack the route response?
It could be done with Rules:


  The Rules module allows site administrators to define conditionally
  executed actions based on occurring events (known as reactive or ECA
  rules). It's a replacement with more features for the trigger module
  in core and the successor of the Drupal 5 workflow-ng module.



set up a field for the user, boolean and use Field Permissions to hide it from users:



  The Field Permissions module allows site administrators to set
  field-level permissions to edit, view and create fields on any entity.



Rules, Event - Drupal is Initialising
Condition - Data field is empty, user field previously set up
Action - redirect to form


Then you can set up an override for the form submit to set the user data field (or use Rules to do it), so that the condition is no longer met.