Although such functionality is not supported out of the box, you can technically achieve the desired result. For the purpose, you need to implement a custom connection that has collections of incoming and outgoing connections. The solution requires:
custom RadDiagram to create custom connections
custom RadDiagramConnection class to provide the logic for incoming and outgoing connections and update them
custom RadDiagramConnector serving as attaching point for such connections
custom ConnectionTool class to provide custom logic for attaching such connections
Attached you can find a small proof-of-concept project.
Please note, however, that this is not a complete solution and I cannot guarantee it will work in all scenarios, but I do hope you find it a good starting point for future customizations on your side.
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