how to add a layout to another existing layout

[vonCZ]

I'm simplifying the problem here, but essentially I've 2 layouts: a primary, top-level QGridLayout with 2 cells, and a QHBoxLayout with buttons. I want to add/put the HBox layout inside the QGrid layout. I see how I can do this by placing the HBox layout inside of QGroupBox 'container', and then

QGridLayout->addWidget(QGroupBox);

...but how can I do this without using the GroupBox?