How to partially mock an existing object

test.php

<?php
$documentExtractor = new DocumentExtractor(
  $ftpDir,
  sfConfig::get('sf_test_dir').'/web/documents'
);

$mock = m::mock($documentExtractor);
$mock->shouldReceive('getDistantControlDir')
  ->with(true)
  ->andThrow('sfException', 'Mock exception');