Filter to modify the_permalink not working WP3.6

Looking for suggestions on how to fix a filter that’s part of a custom plugin. The filter modifies the_permalink and with changes in WP3.6 it no longer works. WP3.6 core now wraps the_permalink() in the esc_url() function.

From /wp-includes/link-template.php:

function the_permalink() {
     echo esc_url( apply_filters( 'the_permalink', get_permalink() ) );
}

The filter I have, maybe is a bit of a messy hack but did work up in prior WP versions, that appends ” target=”_blank” to the the_permalink based on a var set in the custom plugin,

function append_link($the_permalink){
      global $win_target;
      if ($win_target != NULL){
           $the_permalink = $the_permalink . "\" target=\"" .$win_target;
      }
      return $the_permalink;
  }

The esc_url() function is stripping out the double quote and space which ends up with just “target=_blank” tacked onto the end of the url.

Thoughts on how I might repair this filter short of editing the core files or page templates.

Thanks!