How to achieve drill through on Sub Totals and Grand Total

[cognosr]

We are facing issue in making drill reports for totals and sub totals
in list and crosstab reports.
The scenario is as follows -

There is 3 level tree hirarchy to the left side of the crosstab (A1;
B1,B2; C1,C2,C3,C4,C5,C6)
Drill through is needed on Sub Totals and Grand Total.
We are trying to pass A1,B1,C1,C2,C3 for Sub Total1 but all the values
are not getting passed as sub total is not linked to any columns in
the hirarchy.
Please let us know how to achieve drill through on Sub Totals and Grand Total.