Adding Management of Column Totals within Reports for Formulas

Currently, there is not an option to create a formula for the column totals when a user is building a report. The current options are SUM, AVERAGE, MIN, MAX (screenshot below). This added feature would be helpful when a user is trying to calculate the weighted average of a field, not only the sum or average. 

Case: Hours Worked on a Project and finding the weighted average (see screenshots)