You can handle the OnClientLoad and OnClientSelectedIndexChanged client-side events of the control, in order to check if the defaulted selected item is disabled and style the input of the control. In the attachment you can find a simple example on how this could be achieved.
Regards,
Nencho
Telerik
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 Feedback Portal
and vote to affect the priority of the items