WordPress: "Template Redirect" para singles de diferentes categorias

function redirect_singles() {
    if(is_singular()){
      $category = get_the_category();
      $currentcat = $category[0]->slug; //verifico o slug da categoria
      if (file_exists(TEMPLATEPATH."/single-$currentcat".".php")) {
          include(TEMPLATEPATH."/single-$currentcat".".php");
      }
    }
}

add_action('template_redirect', 'redirect_singles');