In general you could use domain method in the code-behind of your page. In order to do that you could handle some of the various OpenAccessLinqDataSource events
that are used to customize the behavior of the control.
For your convenience I created a sample application demonstrating how to handle the Selecting
event to populate the data source from domain method, please find it attached. Bear in mind that the example is using the AdventureWorks database
and its upsGetEmployeeManagers
Let me know whether this helps or if I can assist you further.
the Telerik team
Telerik OpenAccess ORM Meets ASP.NET Web API. Read more.