I have a workaround, though it's not great. Haven't quite figured out how to force the ChartPanel to increase/decrease it's insets to make room.
However, what you can do, is create an additional dataset for the chart. It will not hold any data, it's only purpose is to give you a way to add an additional range axis on the right.
Create an additional y-axis. Set the following properties of the axis:
Axis Label: (Empty String)
Tick Label Color: Transparent
Tick Marks Visible: False
Axis Position: Bottom/Right
Then in the dataset properties set the Y-Axis of your new dataset to your new Y-Axis. This will have the effect of adding more space on the right side of the chart.
A pretty hacky solution, but it works.