How to modify cell before SSRS totals your rows

[tfstom]

I have some cells that are duplicate values.

I can blank or zero out a cell by comparing it to the previous column (using Previous() or a code method.

The problem is that the summing seems to be done before these expressions or code are applied. So even if I clear the cell, the original value is still totalled in my total row.

Is there a way to prevent this?

Thanks,

Tom