Nevermind, this won't work.

The wp_cache_* functions are effectively pluggable and it is expected the drop-ins will define them. A persistent drop-in that doesn't support group flushing would need to be updated to match hacking the groups with the last_changed key.

I'll continue investigating using an action on the last_changed key to allow drop-ins to hook in to that to trigger a group flush.

add_action(
  'wp_cache_set_last_changed', 
  function( $group ) {
    global $object_cache;
    $object_cache->flush_group( $group );
  }
);

Sadly this will not work 😢