This should work:

// override SimplePie_Item

class SimplePie_Item_filter extends SimplePie_Item
{
	function get_title()
	{
	    $title = parent::get_title();	
		if(!$title)
			return null;
	    $title = filter_evil_words($title);			
		return $title;
	}
}

$feed = new SimplePie();

// tell SP its got class
$feed->set_item_class('SimplePie_Item_filter');

// mitt romneyyyyy
$feed->init();

...

// nuke those bad boys

function filter_evil_words($title)
{	
	$evilwords = '(microsoft|riaa|mpaa|osama|putin|circularreferences|memoryleaks|pita|rubyoncrack)';
	$pattern = "/$evilwords/is";
	$replacement = '';
	$filtered = preg_replace($pattern,$replacement,$title);
	return $filtered;
}