I have to go somwhere right now, but the ExecuteCommand widget has "subwidget" accessibility. So you can get to the text widget with

my $dtext = $executecommand->Subwidget('text');
$dtext->configure(
                            -background => 'black',
                             -foreground => 'green',
                             );
[download]

So you probably could work out some way to hold your scroll position. You can get to the widget, so now your question is how to controll your scroll in a text widget. Off hand I would say when you press your button, get the lastline of the textbox at that moment, and run some timer, to hold you there. Over on comp.lang.perl.tk there is a fellow named Jack D., he is the textbox wizard. Maybe ask there, if no luck here.