Hello Andrei Rinea,
No , there is no easy way to implement this. You can try to play with the style of the item that you want to be disabled and use its PreviewChecked and PreviewSelected events in order to simulate its disabled behavior.
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!