Dude ... the whole point was to only use `get_instance()`.

    function set_value($field = '', $default = '', $is_textarea = FALSE)
    {
        $CI =& get_instance();

        $value = (isset($CI->form_validation) && is_object($CI->form_validation) && $CI->form_validation->has_rule($field))
            ? $CI->form_validation->set_value($field, $default)
            : $CI->input->post($field, FALSE);

        return form_prep($value === NULL ? $default : $value, $is_textarea);
    }

Shorter, faster.