Unfortunately we do not provide such control because of the limitations of the Silverlight runtime: natively HTML can be displayed only in out of browser applications, otherwise you need windowless to be able to put an IFRAME over the Silverlight plugin.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items