An 'Overall Total' label on top of a stacked column or chart

Description:

I would like to add an "overall total" data label to the top of a stacked column or bar chart.

Example:

We are looking at whether our new Agreements come from Existing Customers, Previous Customers, or Brand New Customers. But I also want the overall total represented on the graph as a data label.

Benefit/impact: 

Spotlights where the store's marketing strengths are, weaknesses, and where they need to focus their attention towards.