I need to know the same thing. Did you ever figure this out?
If you are looking for following kind of graph, you can replicate it using one Calculated field.
Step1. Create the following calculation “Top 80” ( I have replicated using Country/Region in Super Store DB)
If RUNNING_SUM(SUM([Profit])) / TOTAL(SUM([Profit]))<=.8 then Attr([Country / Region])
Else 'Others' End
Step 2. Create a simple Bar chart on Total profit on rows
Step 3: Drag your “Customer Dimension” into the Detail Shelf
Step 4: Sort the Detail shelf “Customer Dimension” descending order by Profit
Step 5: Drag the “Top 80” Calculated field to the Color shelf.