Using ReportBook is not possible with UriReportSource, you have to deserialize the .trdx file to a report object in order to add it to a ReportBook. See this thread: http://www.telerik.com/forums/add-urireportsource-to-reportbook.
It would all be so easy if there was some kind of "here-you-find-all-your-report-files" property somewhere... So what is the
SOLUTION?