How to sum the data labels to a total in my chart diagram?

Hi

I am counting order type by a field which can have 3 different values.In a stacked column chart I am displaying the count of those different values, and showing a data label with the count for each order type. See screenshot.

Now I would like to show a line based on the total of each order type. I can see that SSRS already know the number of each order type as it is shown in the labels. How do I add those numbers (shown in the labels) together and get it into a Total field? I would prefer not to alter my SQL query, if possible.