QwtPlot::insertLegend() does 2 things:


  1. inserting the legend into the layout system of the plot
  2. connecting the QwtPlot::legendDataChanged() signal with the QwtAbstractLegend::updateLegend() slot


As you don't want (1) I would simply do (2) in application code. Then you can use a QGridLayout with 2 columns putting the plots in the left and the legends in the second one.
( Don't forget to set QwtLegend::setMaxColumns() to set up the number of entries per row inside of the legend ).

Uwe