Place uploaded files outside public_html

Hey there.

I am using the following filter to place files uploaded through a ACF file field in a subdir to uploads. However, I would like to place the files outside public_html instead. Is this somehow possible?

upload_dir() seems to take ../ quite literally..

add_filter('acf/upload_prefilter/name=fieldname', 'field_name_upload_prefilter');

function field_name_upload_prefilter($errors) {
  // in this filter we add a WP filter that alters the upload path
  add_filter('upload_dir', 'field_name_upload_dir');
  return $errors;
}

// second filter
function field_name_upload_dir($uploads) {
  // here is where we later the path
  $uploads['path'] = $uploads['basedir'].'/subfolder';
  $uploads['url'] = $uploads['baseurl'].'/subfolder';
  $uploads['subdir'] = '';
  return $uploads;
}