Group release phases by month start and end date for reporting

Our primary executive report (currently in Excel) includes a list of features and releases down the rows, with the columns being a month (January, February, etc.). Each cell shows the milestone for that initiative (Alpha, Public Beta, GA, etc.) so one can view a cascading report of major milestones for each feature/release on the roadmap. I need to create a similar report in Aha and not being able to group Pivot columns by Release Phase/Milestone Month is a blocker. Until then, our primary exec roadmap unfortunately remains in Excel.