Hello varnguyen,
There is no API option that could do that, but it is possible. My idea was to initally align all stack labels to the left side, to make sure that they are aligned in one line, and then translate whole group to the right site of the chart. Effect looks good to me and what is more important, the solution is responsive.
Demo: https://jsfiddle.net/BlackLabel/u8afhyLs/
API reference: https://api.highcharts.com/class-refere ... #translate
Let me know if that was what you were looking for!
Best regards!