Stacked Heat Map in highcharts

Question

I would like to create a stacked heatmap. basically i have sub categories, I would want to show in a Heatmap. After searching I figured it is not possible to do.

So I am wondering if it is possible to create a stacked heatmap instead where sub categories would be stacked on top to make a category. A mixture of bar chart and heat map.

Please see the fiddle .. As a an example I tried to attain the objective with multiple series. As you can notice if the series have same values they just sit on top of each other. Is there a better way to visualize such a data ?

Heatmap take x,y,value. If a data had x,y,value AND Z .. What would be the best way to visualize in highcharts?

Thanks..