Using a Cocoa build of Qt:

• Add some shortcuts to a QMainWindow's menu
• Override event() method in a child widget of that window as such:

bool MyWidget::event(QEvent *event)
{
    if (event->type() == QEvent::ShortcutOverride)
        event->accept();

    return QWidget::event(event);
}

Works as expected on Windows (main window shortcuts won't be triggered), but seems to do nothing whatsoever on OS X.