Make some plot, with a legend:

Make another plot, with its name, but do not add the legend yet (or it would go into the first legend box): Now create the second legend box, at location [0,0.5], adding the last plot to it - this must be done at a time when there is a plot object selected (as is the case just after a plot is created): Now create another plot, and add it to the second legend box - the item to be added to the legend is the currently selected one: The result should look like