Adding Sub Calculations to Pivot Table

Why not just have formulas to the right of the pivot table to show the calculations?

You can make the blank cells empty and you can use conditional formatting to make it look identical to the pivot, so they wouldn't know.
Or you can use simple VBA to literally copy and paste formatting after dragging formulas down to the bottom of the pivot. I have done that previously.

the macro would do whatever the pivot does.

I would have a formula copied and pasted to the bottom of the pivot, then copy and paste formatting across the entire range for all your copied down formulas. You could even copy and paste VALUES at the end so the user has no idea it is/was a formula.

You would do a macro fired off an event, pivot update or whatever. so they never even click a button.

Ha, well I would send you one of my examples but I am on my phone waiting on a gym partner. o_O

Essentially you figure out whatever formula you need to the right for the percentages and such and have them either stored in the macro or in row 1 or in a REFERENCE worksheet hidden in the background, wherever you prefer.

So you have a macro automatically fire off when the pivot table is refreshed or updated using the EVENT (you will have to put the code in the worksheet area not in a general module).
Once the macro fires off, you clear all the formulas/values to the right, leaving your headers you manually created (or you can store the headers with the formulas on your references worksheet)
You count how many rows the pivot table has after update
You drag the formulas down to that number of rows
You copy and paste formatting from the pivot table
Then you can copy and paste values if you want

Then you end the sub. This allows filters and slicers to control all of it...

This is likely the event you would want to use.
https://msdn.microsoft.com/en-us/lib.../ff822105.aspx