Hello Laijun Xie,
We are currently developing such functionality which is available in the our Latest Internal Build
. I am attaching a simple project showing how this can be achieve. Please note, that due to a known bug currently in WPF the LinearDropVisualProvider is not shown, but you can see how it should behave in the Silverlight project. The behavior should be good to go for our next major release.
the Telerik team