Well, I'm not sure this is the best solution, but it works. You can't have the -expand=>1 -fill=>'both' on the $spane, it interferes with the scrollbar calculations. And you need to set a height for the Pane. There probably is a way to calculate the needed height, but I just hard coded in 400 pixels.

my $spane = $mw->Scrolled('Pane', 
        -scrollbars => 'oe', 
         -height => 400,  
         -bg => "orange",  
         )->pack();    

my $yscrollbar = $spane->Subwidget('yscrollbar'); 
$yscrollbar->focus;   #makes up/down arrows control scrollbar
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