Hi Virginia,
Somewhere in your code you set the datasource at runtime, Right? That datasource is the EntityCollection you fetched using an adapter, Right? So when you fetched it you include a PrefetchPath, Right? In that prefetch path object you indicate how deep you want to fetch the related entities. If you use adapter this is the normal way to go.
Are you doing something different? If so please give us more information about the routine which fetches the entities.
Also, I'm very confident that the setup you can do on infragistics control at design time, you could also do it in runtime. It's a matter of finding the way in their documentation.