That 's really a nice question. So far from what I have seen, it is possible but let me sometime to write a sample code to test before answer you.

Hi Elcid,

Please download our latest KoolReport package and try the following code:

use \koolreport\core\Utility as Util;

...
->pipe(new Sort(array(
    'sales' => 'desc',
)))
->pipe(new Map([
    '{aggregate}' => function($row, $meta, $index, $data) {
        if ($index >= 5) {
            $sum = Util::init($data, 'others', []);
            foreach ($row as $c => $v) {
                Util::init($sum, $c, 0);
                $sum[$c] = is_numeric($v) ? $sum[$c] + $v : 'Others';
            }
            $data['others'] = $sum;
            return $data;
        }
    },
    '{value}' => function($row, $meta, $index) {
        if ($index < 5) 
            return $row;
    },
    '{end}' => function($count, $data) {
        return $data;
    },
]))
->pipe($this->dataStore('myDatastore'));

Please remember to change the "sales" field to your data column. Let us know if you have any problem. Thanks!