I need to get my pivot table to return a percent of subtotal instead of a
percent of column. Here's what I want:

Region State Sales Percent of Sales
North Montana 10 10 %
Idaho 90 90 %
North Total 100 100 %
West Calif 50 25 %
Oregon 100 50 %
Arizona 50 25 %
West Total 200 100%

I can easily do this using the Show Value As % of Column option with field
settings for the Sales Field, but as the description implies this gives me
just the percent of of the grand total for the column rather than for the
subtotals.
Is it possible to do what I want here?