public class XYZPart {

    @Inject
    public void init(BorderPane pane, XYZController controller) {
        pane.setCenter(controller.getRootNode());
        // further calls on the controller instance
    }
}

public class PartRendererAddon {

    private EventHandler eventHandler;

    @PostConstruct
    public void execute(final IEventBroker eventBroker, @ContextValue(contextKey="controller") ContextBoundValue<XYZController> value) {
        eventHandler = new EventHandler() {
            @Override
            public void handleEvent(final Event event) {
                // not sure if this is the correct property
                Object part = event.getProperty(UIEvents.EventTags.ELEMENT);
                if (part instanceof MPart) {
                    renderPart((MPart) part, value);
                }
            }
        };
 
        // not sure if this is the correct event
        eventBroker.subscribe(UIEvents.UIElement.TOPIC_WIDGET, eventHandler);
    }

    private void renderPart(MPart part, ContextBoundValue<XYZController> value) {
            String controllerPath = getControllerPath(part);
            Object controller = loadFXML(controllerPath);
            // add to the context
            value.publish(controller);
        }
    }

    private Object loadFXML(final String path) {
        FXMLLoaderFactory fxmlLoaderFactory = getFXMLLoaderFactory();
        // load FXML and return controller instance
    }

    private FXMLLoaderFactory getFXMLLoaderFactory() {
        //
    }

    private String getPath(final MPart part) {
        // calculate path to FXML based on part's name
    }
}

public class RootPresenter {

    // field declarations...

    @PostConstruct
    public void init(BorderPane pane, @FXMLLoader FXMLLoaderFactory loaderFactory, HeaderPresenter headerPresenter) {

        Data<Node, RootController> data = loadFXML(loaderFactory);
        pane.setCenter(data.getNode());

        RootController rootController = data.getController();
        HeaderController headerController = rootController.getHeaderController();
        headerPresenter.setController(headerController);
        headerPresenter.init();
        // do more meaningful stuff with the sub-presenter or the controllers...

    }
}