How to use Aggregated Summary amount as part of a Percentage column

[nbailey]

I am trying create a percentage column in my Cross Tab Report using a cell member and the Aggregated total from the same measure .   How do I capture the aggregated total and use it as a second measure column to create the percentage.   
See percent col below...  how do I capture the item total as part of the aggregation and use to create percent total (1/6 for item1 and etc.)   see enclosed example for additional info.

                             amt col           percent col
dbname1  item1       1                   item total/item1     
                 item2       2                  item total/item2
                 item3       3                  item total/item3
           item total      6     

dbname2  item1       4                   item total/item1
                 item2       4                  item total/item2
                 item3       4                  item total/item3
           item total      12     
dbname total