Currently it is not possible to show the filter row until some data has been received and the dropdown is visible. Please enhance/change the DropDownList widget so that it will be possible the enter a filter expression before any data is queried. Related forum post: http://www.telerik.com/forums/server-filtering-how-to-not-query-data-until-filter-has-been-provided
Hello,
This functionality has been added in Q1 2015 SP1.
Regards,
Ivan Danchev
Progress Telerik