How can I increase the chart area without increasing or
reshaping the plot area itself?

Forgive me if my terminology is wrong and confusing.
By "chart area", I mean the white area around the plot
area. By "plot area", I mean the area between the X
and Y axes.

My list of series is so large that it is clipped by the
current chart area. When I drag the chart area handles,
that also resizes the plot area. I want to avoid that.