Adding gap between specific bars in a stacked bar chart - highcharts

Question

I have two groups of stacked bars in a chart and I would like to group them visually
So how could I add extra vertical gap between specific bars in a stacked bar chart or separate the groups in some other way?
Example:
http://jsfiddle.net/KrTbz/41/
I would like to add extra vertical space between bars 4 and A
new Highcharts.Chart({
chart: {
renderTo: 'container',
type: 'bar',
},
title: {
text: 'Grouping test',
},
xAxis: {
categories: ['1', '2', '3', '4', 'A', 'B', 'C', ]
},
plotOptions: {
series: {
stacking: 'percent'
}
},
series: [{
name: 'Alpha',
data: [31, 27, 23, 22, 22, 20, 21]
}, {
name: 'Omega',
data: [5, 6, 7, 5, 6, 6, 5, ]
}, {
name: 'Gamma',
data: [60, 62, 67, 69, 68, 70, 71]
}]
});
});

Answer 1

It is not possible in simple way, but only what comes to my mind is quite dirty solution but maybe will be enough. So you can set null values in series and in categories.
http://jsfiddle.net/KrTbz/42/
xAxis: {
categories: [ '1','2','3','4','','A', 'B', 'C', ]
},
series: [
{
name: 'Alpha',
data: [31,27,23,22,null,22,20,21]
}, {
name: 'Omega',
data: [5,6,7,5,null,6,6,5,]
} ,{
name: 'Gamma',
data: [60,62,67,69,null,68,70,71]
}
]