public class MyGef extends GraphicalEditorWithFlyoutPalette implements ISelectionListener{
     public void selectionChanged(IWorkbenchPart part, ISelection selection) {
	super.selectionChanged(part, selection);
	
  	IStructuredSelection incoming = (IStructuredSelection) selection;
     }

}

figure.addMouseListener(new MouseListener.Stub() {

    @Override
    public void mousePressed(MouseEvent me) {
	if ((me.getState() & MouseEvent.CONTROL) != 0) {
	    // figure was selected while CTRL key was pressed
        }
    }

});

public class YourEditPart extends AbstractGraphicalEditPart {
    ...

    @Override
    public DragTracker getDragTracker(Request request) {
	return new DragEditPartsTracker(this) {

	    @Override
	    protected void performConditionalSelection() {
		super.performConditionalSelection();
		    if (getCurrentInput().isControlKeyDown()) {
			// the part was selected while the CTRL key was pressed
		    }
		}

	    };
    }
}