display a Calculated Item in Data Label

In a pivot chart I display two values and a calculated item
"difference". I would like to display a third calculated item "%Diff"
as a data label for difference. Right now I accomplish this by
including %diff as a an item in the chart and change it from bar to a
line chart type. Turn of the line and marker and just drag the data
label over the Difference bar.
I I need to make a series of these charts and do not want to have to
"trick" the chart to do this every time.

Is there a better way?
Thanks
Robert