<?php
// set the plugin name and the controllers we want to hack
$rewritePlugins = array(
	'forums' => array('posts', 'topics'),
);
// rewrite it!
foreach($rewritePlugins as $plugin=>$options) {
	$_GET['url'] = preg_replace('%^('.$plugin.')/('.implode('|', $options).')%i', '\\1/\\1_\\2', $_GET['url']);
}
?>