Unfortunately this behavior can not be achieved because single click event is always fired and this make it impossible for the DoubleClick to be handled.
is an article in our help resources, which explains in more details( see Point 3
Hope this will be helpful.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed