Pivote Table Calculation problem

Hi all, I've been working on a pivot table and I'm up against a brick wall at the moment with what I need to do so any help will be much appriciated. (I'm using Excel 2007)

I have a base sheet containing the following column headings:-

Date; Surname; Forname; Sport 70; Sport 50; Skeet 25; ABT 25

These are basically member names and shooting scores.

I have a Pivot table that then takes all of these columns and displays some averages (through the average value field option) to allow the members to be categorised into divisions.

The problem is that we only work on the highest 10 values from all the shoots, so for example member 1 has visited the club 30 times and everytime he has a score in "ABT 25", the pivot table will easily show the members average, however I need it show the average of the members top 10 scores only.

I hope that makes sense if not let me know what info you need any questions etc and I'll post them immediatly. I've attached the sheet for ref.

Thanks in advance Shaun