This is more of a suggestion than a solution. Does it have to be Pie Chart? For Drill-Down/Roll-up the hierarchies "Bar Chart" is the best way to visualize data.
There is however a workaround to get the same in Pie Chart, refer to this thread and see if it works for you.
Hope this helps.
Question.twbx 1.2 MB
Thanks ShivaRam for the suggestion and the link for the thread. I will follow it's steps.