Thanks for contacting us with your question!
Unfortunately, it is not possible to do that in Highcharts, but I prepared a custom solution for you, where you can do it using any key (in this case 'z' key). You can't do it with shift or ctrl because it may interrupt some of the default browser behaviors. Just remember, before you try it, click with mouse on the white window with the chart, unless it won't catch the keydown event.
Let me know if that was what you were looking for!