Have you considered Mike Moyer's method, described in the Slicing Pie? http://slicingpie.com/ http://slicingpie.com/ It is pretty fair and adjusts over the time

Have you considered Mike Moyer's method, described in the Slicing Pie? http://slicingpie.com/ http://slicingpie.com/ It is pretty fair and adjusts over the time based on the delivered values.