Multi Column totals within a Column Group Hierarchy

Hello,

I have hit a wall....working with the tablix.  Screenshots are included below.  The intent is to insert a column to the left of the ztransactiondate column (but remain under the ReportCostCategory group). this column would simply show the current month (March 31, 2013) in it's own column with the totals only for March. Therefore when the reportcostcategory group is collapsed only two columns would remain visible - March and the Cumulative Column.  when +expanded March would still show but all the other months would still show.

Big graphic...hope it is easy to read.

Any help on this would be appreciated.

Thanks,

HPzip