Shared tooltip with multiple stacks

Shared tooltip with multiple stacks

I've implemented a stacked column chart with 4 series divided over 2
stacks. I want to create a tooltip for each stack that only shows info for
the series that belong to that stack. When I use shared: true option for
the tooltip formatter function, I get all the series in the
$.each(this.points, function(i, point) {}) loop.
How can I create a tooltip for each stack, while still having access to
all the series in the stack?
Any advice is appreciated.