I believe that you can achieve the desired appearance by overriding some of the default settings of the RadSlidingZone but I am afraid I cannot completely understand your exact requirement. Would you please prepare a few screenshots and mark the actual and the desired appearance there? Once you do this, just open a new support ticket and send them along with the splitter's definition and detailed explanations. Once I have a better understanding on your exact requirements, I will do my bets to help.
the Telerik team