How to migrate files with file_link?

I am migrating to a custom content type from an external data source. I have the images I want to use stored in a directory on my server but they are vast in numbers. So instead of copying to them, I am hoping to just link to them. I created a symbolic link at /sites/default/files/ that points to the dir with the images.

The following code is not performing like I describe above. It's not linking to any image files at all. Any help would be appreciated.

I'd also like to prevent file deletion on rollback as stated here http://drupal.org/node/1061560, how do I do that within the MigrateFileFieldHandler?

// install file settings for image field in custom content type
Array=(
    'listing_image' => array(
      'field_name'  => 'listing_image',
      'label'       => $t('Pictures'),
      'required'    => FALSE,
      'widget' => array(
        'type'    => 'image_image',
        'weight' => 0.18
      ),
      'display' => array(
        'default' => array(
          'type' => 'galleryformatter_default'
        ),
        'teaser' => array(
          'label' => 'hidden',
          'type' => 'image',
          'settings' => array(
            'image_style' => 'galleryformatter_thumb',
            'image_link' => 'content'
          )
        ),
      ),
    ));

I put the following in my module.inc file

// the following is the field mapping in __construct()
    $arguments = MigrateFileFieldHandler::arguments('/var/www/html/example/sites/default/files/rets_images/resi/', 'file_link', FILE_EXISTS_RENAME);
    $this->addFieldMapping('listing_image', 'src_images')->arguments($arguments);

//This is what I used in prepareRow($row) to pull a list of files and set the image data json encoding
  $row->src_images = array();
  $files = glob('/var/www/html/example/sites/default/files/rets_images/resi/'.$row->listingrid.'*');
  if($files && !empty($files))
    foreach($files as $key => $file){
      $file = str_replace('/var/www/html/example/sites/default/files/rets_images/resi/','',$file);
      $img_data = array(
        'path'=> $file,
        'alt' => $row->src_title,
        'title' => 'MLS '.$row->mlnumber.' image #'.$key+1
      );
      $row->src_images[] = drupal_json_encode($img_data);
    }