// PHP 4 >= 4.0.1, PHP 5
public static function json_encode($array)
{
    return preg_replace_callback(
        '/(?<=:)"function\((?:(?!}").)*}"/',
        create_function('$string', "return str_replace('\\\\\"','\\\"',substr(\$string[0],1,-1));"),
        json_encode($array)
    );
}

// PHP 5 >= 5.3.0
public static function json_encode($array)
{
    return preg_replace_callback(
        '/(?<=:)"function\((?:(?!}").)*}"/',
        function ($string) { return str_replace('\\"','\"',substr($string[0],1,-1)); },
        json_encode($array)
    );
}