Thank you for writing back.
Now I understand your requirement but this functionality is not supported by RadDock. You will have to develop a custom control to get this functionality. If you are to modify RadDock to get this functionality you will spend more time and resources than to develop a new control from scratch. Should you decide to implement such a control I would be glad to assist.
I hope this helps. If you have further questions, I would be glad to help.
All the best,
the Telerik team