Excel 2007 : Pivot table formulas with "custom subtotals"

In my sample file, in sheet "pivot1";
I've created a pivot table and added a formula field into it. It's a percentage (devision) formula. I've colored it with green in my sample file. And I have subtotals which show the sums of years, colored with red. These work fine.

In sheet "pivot2";
I used "custom subtotals" (my Office is not English so I translated it directly) to be able to see both the SUMS and the AVERAGES. And the formulas in subtotals disappeared.

Looking at my file you can understand more clearly.

How can I make the formulas work with "custom subtotals"?

(I hope there won't be a compatibility problem about the language... Everything I used is English but I don't know if the formulas will be compatible or not.)

For those who don't have Office 2007, I've attached 2003 version of my file.

Any ideas ???