I think the better solution would be to use 2 pie charts, in the first group all < 5% clients in one category "Other". In the second just map other. (again grouping clients < 5% of the other category, but not mapping them).
I think the suggestion to use a timeline series is not a good idea, pie charts are perfect for visualizing complementing percentages.
If you really want to visualize the movement of the percentages use a stacked percentage chart like this one:
Like these: http://smoothiecharts.org/ or http://www.highcharts.com/demo/dynamic-update