A quick follow up.
We will do our best to provide this functionality for the upcoming Service Pack. In case the source code could not make it for a check-in before the code freeze for the Service Pack, it will be released immediately after that with the first "Latest Internal Build' after the service pack. I hope this helps.
All the best,
the Telerik team
Browse the videos here>>
to help you get started with RadControls for Silverlight