Custom Others or Total calculation in straight table

[#1]

Is there a way to customize the Others or Total aggregation in a straight table?

What I want: max(.15 - TotalSales / TotalSectorSales, 0) * TotalSectorSales where Total Sales = Sum_{c in companies} (Sales_c) and the same for sector sales

QV seems to do the aggregation this way:

Sum_{c in companies} ( max(.15 - Sales_c / SectorSales_c, 0) * SectorSales_c)

Your help is greatly appreciated.