Adding percentage calculation to Sage 50 P&L Report

I want to modify the Profit and Loss (Actual Budget & Variance) Report  so that it shows the percentage of one detail line total as relating to the total Category cost of a different Category.  Its a variant of the calculate costs as a percentage of total sales type of facility.In this case the Sales Category contains several lines of detail, one of which Sales Type A is the divisor.  The second Category is Direct Labour, comprising Labour Type 1 and Labour Type 2.  I want to define an expression which will calculate the Direct Labour Category cost as a percentage of the Sales Type A, for the actual and budget, this period and year to date.

Can this be done?