Column Totals - can they be specific to the category?

I have a categorised view, containing three subcategories. In this view, there is a totals column. At the moment, this column produces totals for each category, showing everything. Is there a way that I can change this column so that it will only show the total for one of the categories?

For example, if I have all columns categorised, we have Column 1 total, Column 2 total, Column 3 total. I would like Columns 1 and 2 to be ignored, and only the total for Column 3 to be displayed in the view.

Does that make any sense? Can it be done?

Many thanks!

Alex