Custom Subtotal

Hi,

I am using a matrix to report, and there is 2 rowgroups and onde column group. It looks like this:


T1 T2 T3 T4
type1 A 9 3 2 4
B 6
type2 A 1 2 3
B 2 4 1 7

But I need to sum only 2 columns of the report (columns T2 and T3):



T1 T2 T3 T4 T2+T3
type1 A 9 3 2 4 5
B 6 6
C
type2 A 1 2 3 2
B 2 4 1 7 5
C 8



And I do not know how to create this sum column, only the default sobtotal column of a matrix.
I tried to do this sum in my datasource, but with no success too.
I also tried to use a table, but the columns must be create automatically from database data and I couldn't do it.

Another issue is: how to make line C appear even with only null or zero numbers?

Any ideas?

I am new with reporting services, so please be clear and detailed.

Thanks a lot!