Is this possible?

I have three items in my pivot: Department, 2012Amt and 2013 Amt. I added Dept to the row area and 2012Amt / 2013Amt to the data area of a pivot. I then added 2012Amt and 2013Amt second time but this time set each to be a % of the total.

So I now see each dept, it's 2012 amt, it's 2013 amt, it's 2012 amount expressed as a % of all depts and its 2013 amt amount expressed as a % of all depts.

I have been asked to add another column that shows the difference between the two % columns. However they want it part of the pivot...NOT using formulas outside the pivot....essentially they want they want the the delta of the %s shown.

Can this be done?