We understand your custom scenario. Unfortunately, with the current implementation the required behavior is not supported out of the box. Also, we cannot say if that is possible to achieve with the RadDiagram
control. It depends on your custom scenario.
If you need to visualize the curve for limited number of shapes, you can recreate it with a floating Spline
connection with three points (StartPoint, EndPoint and MiddlePoint).
If you need that curve to be fully functional and users to be able to interact with it, there might be difficulties in achieving your requirement.
However, in both cases we need more detailed specifications on the required behavior (the more detailed they are, the better) to evaluate if it is achievable. Please provide us with more details.
Pavel R. Pavlov