Averaging actual costs over a long activity is awful

I've been trying to set up P6 to track and forecast a 5-year program with 15 subconsultants for a major transportation agency in the US.  I just figured out today that if I have a long activity (and many of the administrative support tasks are LONG LOEs), and the rates change during the course of that activity, that I can't store the cost at any given point in time.  P6 averages the rates over the duration of the activity which makes reporting for a defined financial period completely useless.

What is so frustrating is that with timesheets the program does exactly what I need it to do.  Actuals are recorded by individual day, that individual day checks the effective date for a resource cost, and it calculates it correctly.  And I can report on that.