Currently, you can use formulas in the pivot table chart to create new calculated columns. I think it would be a good idea, and extremely useful to than run other calculations off those new calculated columns (currently unavailable as a feature).

Example:

Data Set Column 1 + Data Set Column 2 = Calc Column 1. (currently available)

Data Set Column 3 + Calc Column 1 = Calc Column 2. (feature request)