Most of the time with graph builder you might be able to get away by using Color or Overlay (depending on the plot).
In some of the other platforms (not sure if this works in all of them) I think you have to start from those platforms and create legend there from right-click menu
With scripting you might be able to move the legend window, but I'm not sure how well it would work. Best way might be dependent on the graph/report/platform/what to display in legend.
-Jarmo