Adding Calculated Fields/Formulas to a Pivot Table

I have a pivot table that summarizes how many billable and non-billable hours each sales person spends on their clients per week. Each sales person has a section of rows with the projects they've been working on in each row. The table values are the hours per project per week for each person. There is a column for each week, then the final column is the total number of hours for all weeks per project, and a row with the grand total number of hours worked on all projects over all weeks per person. What I want to do is take the total hours spent for all weeks on each projects and express that as a percent of grand total hours for each person. Since that's probably pretty hard to visulize, I've attached a sample picture! The column I want to add (which is currently outside of the pivot table) is H.

I can make this happen by manually entering formulas in column H outside the pivot table, but can't for the life of me figure out how to create a formula - either outside the pivot table or inside as a calculated field - that I don't have to enter manually for each row. Can someone please help! I'm dying over here!