Pivot-Sort by Grand Total column

For a two-column pivot (one Data field, one Row field) I can sort the Grand Total column by highlighting the Row and Data ares and doing a Sort by column B. But how do I sort by the Grand Total column when I have a more complex Pivot Table? For instance, in the attached example, within each Unit I'd like to be able to sort by the number of FTEs in that unit. How would I be able to do that? And how about even more complex pivot tables?

Your help is greatly appreciated.

Thanks,
John