How to ignore specific Drupal release in update notifications?
Note: this is definitely not recommended. Hiding security updates is bad for all the obvious reasons (it's clear you know that, but for the sake of others who see this...).

As a technical exercise, I can't see why something like this wouldn't work (un-tested):

function MYMODULE_update_projects_alter(&amp;$projects) {
  $projects['system']['info']['version'] = '7.29';
}


That should basically trick Drupal into thinking core is already at 7.29, so you shouldn't get any warnings. Plus you should also receive update notices for 7.30.