Note that set_dropZones is not currently working as one might expect. In order to set drop zones dynamically on the client, you must call a hidden function to initialize the drop zones (Nencho at Telerik provided this workaround):
functionAppLoaded() { varasync = $find("<%= RadAsyncUpload1.ClientID%>"); async.set_dropZones("#dropZone1,.otherDropZones"); async._uploadModule._handleCustomDropZones();}Sys.Application.add_load(AppLoaded);
Thank you, Nencho.