QML How to paint different to grabToImage()

Is there any possible way to make grabToImage() buffer different from what's displayed in GUI? I'm using ChartView without legend in GUI and want to export it to PNG with legend. So I try:

chartView.legend.visible = true
chartView.update()
chartView.grabToImage(function(result) {
    console.log("grabbed")

    var path = filename.toString().replace(/^(file:\/{2})/,"");
    console.log(path + result.saveToFile(path));
    chartView.legend.visible = false
    update();
});

But both those updates happen only after the control comes out of this function, so I don't get legend drawn in PNG. Also I would like the appearance of legend to be unnoticable to user. Are there any ways to do that in QML?