Add column to give average in a hierarchical model

Hi,

I have the following scenario in a sales company:

It's a hierarchical sales team where a few executives are under a Team Lead. A few Team Leads work under a Manager.
In the attached spreadsheet, sheet 2 gives a detail of the sales value for each sales executives for each month. In the sheet 1 i have a pivot table to calculate Average Sales per executive and per TL and per Manager for each month.
While i am able to calculate the same for each month. I am not able to calculate the same(Average sales for Executives/Team Lead/Manager) for the entire period consolidated. Can you please help?

I dont want to create the aggregated column in the detail report. We need to have this only in the pivot table.