Is there any way to have custom ways of summarizing data in a pivot table?

I have some grouped values etc, and I want the average for each group and
the MAX of the group minus the MIN of the group.

It seems that you can run a formula on each individual row that gets entered
(though I haven't figured out how), and you can run a formula on the SUM of a
certain group of data, but you don't seem to be able to, say, subtract the
MIN from the MAX of a group of data. The summary functions listed include
SUM, COUNT, VAR, MAX, MIN, etc, but I can't see any way of combining these.

When I enter a formula and do Column1 * 5, it gives me the sum of each
Column1 group * 5, when I do COUNT(Column1) it gives me 1, etc. I want
MAX(Column1) - MIN(Column1) to give me the max of the group minus the min of
the group.

Does anyone know the most elegant way to do this?

Thanks a lot,
Kestas