Found the answer on a 6 year old mailing list thread, here's the code, but now working. The same glade file

#!/usr/bin/perl
use strict;
use warnings;
use Glib qw/TRUE FALSE/;
use Gtk2 '-init';
use Gtk2::SimpleList;


# Connect to the glade file
my $builder = Gtk2::Builder->new ();
$builder->add_from_file ('example.glade');
$builder->connect_signals ();
 
# connect to the combobox
my $cbox = $builder->get_object ('combobox1'); 
my @listing = qw/random stuff just to test /; 
my $text;

my $model = new Gtk2::ListStore('Glib::String');
$cbox->clear();
my $renderer = new Gtk2::CellRendererText;
$cbox->pack_start($renderer, FALSE);
$cbox->set_attributes($renderer, text => 0);
$cbox->set_model($model);

# This is supposed to append the @listing to the
# combobox
foreach $text (@listing) {
    $cbox->append_text ($text)
}

$builder->get_object ('window1')->show_all;
Gtk2->main;
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