Have you had a look on Qlik Branch to see whether there was anything suitable. Been working through some of the challenges of stacked bars in Sense and I had to make some minor adjustments to the already available extension objects on branch.
If you are able to have a go at modifying the extensions in Dev Hub this maybe the best option. Otherwise I am happy to assist.
I found an extension which is having bar chart stacked. It is based on chart.js.
When I am creating chart using it is having option of showing label but even when I turn it on I am unable to see the values.
Here is the url of extension- http://branch.qlik.com/#!/project/576bab2754cc348900aeb122
I am not very familiar with JS so I am facing problem to identify the required change in the extension.