Export custom column in highchart csv

Highcart is great library for creating charts. There is export plugin which provides feature to export chart data as csv file. In last project I need to compute a new column when exporting data from chart.

We can do that by manipulating the series of chart. Below is example code:

var series = [{
  name: 'A',
  points: [{
    x: 10,
    y: 30
    x: 13,
    y: 50
    x: 15,
    y: 25
  options: {
    stickyTracking: true
chart.series = series;

Full jsfiddle exmaple can find here. (http://jsfiddle.net/crazyrohila/akrayjtq/)