Custom Formula in Pivot Table Row

Hello all,

I use Pivot Tables (Excel 2003) to create Profit & Loss statements.
I would like to insert a custom formula to calculate 1) Gross Profit
and 2) Gross Profit %.

My pivot tables look something like this:

Acc Type Account Budget Actual Variance
Sales 5001 | 10000 12000 2000
5002 | 5000 4000 -1000
5003 | 2000 2500 500
-------------------------------------------------
Sales Total 17000 18500 1500
-------------------------------------------------
COS 6001 | 8000 8500 500
6002 | 2000 1500 -500
6003 | 500 1200 700
-------------------------------------------------
COS Total 10500 11200 700
-------------------------------------------------
Grand Total 27500 29700 2200


What I want to do is to rename the "Grand Total" row to "Gross
Profit".
Then, I want this row to subtract COS Total from Sales Total (for each
column).
I don't want to use a formula row outside of the pivot-table.

Is this possible?

Cam