1. A custom report template is checked for getting the data source information needed
2. A new empty Telerik report is created
3. The report is client-side filled with those predefined data sources using the Telerik Javascript Shell (EditorCommand.NewItem for creating them and SetPropertyValue for filling in the details).

This approach has been working well for me until getting updated to the R1 2021 SP1 release (15.0.21.224), or the following versions, which are now unable to show the datasources fields in the explorer at first. However, manually adding a new component into the canvas makes the datasource tree to be updated then.