The Scopes already support multiple inputs, just go to the Scope parameters and choose the number of axes (double click on the scope to get the graph up and click the second icon on the toolbar (the one next to the printer))
You can also have a look at the floating scope, bring the graph up and click on the graph, that will open a window where you can select the input signals, no connection will be made to the floating scope but it will draw the selected signals.
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