I'm no Tk-specialist either but I think you will need a
Text or a
TraceText widget for that.
TraceText looks especially promising as you can bind a Perl-variable to the contents of this widget, so if you set the content of that variable prior to calling Tk, it should show your "pre-set" value.
CountZero
"If you have four groups working on a compiler, you'll get a 4-pass compiler." - Conway's Law