Allow Pivot summarized values to be used in calculations

When using the Pivot to summarize a set of records I need to use the derived valued to compare against another, like what you can do in Calculation columns. Since the pivot creates this value based upon a grouping, for example all children records, I need to compare this value to a field on the parent. Worksheets do not work in this case as I'm using an Aha! record relationship field.