I googled for something, and it seems you can put a tooltip on a TreeView, see
tooltips on treeview workaround . Since the perldoc for Gtk2::Ex::SimpleList says you can make a SimpleList from a Treeview (or derive the parent Treeview), you may be able to use that fact, to put the tooltips on the underlying TreeView. I guess one of the things on their to-do list, is to make tooltips more easily integrated into the TreeView widget. You might also ask on the gtk2-perl maillist.
You can add a tooltip to the entire SimpleList widget, as shown below, so you might be able to somehow connect mouse motion to the nearest entry, and modify the tip-text dynamically.....but I'm just brainstorming.
Also remember, that there is a difference between Gtk2::Tooltips and Gtk2::ToolTip.
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
use Gtk2 '-init';
use Gtk2::SimpleList;
use constant TRUE => 1;
use constant FALSE => 0;
my $categories = Gtk2::SimpleList->new ('Categories' => 'text');
$categories->set_headers_visible(FALSE);
@{$categories->{data}} = qw/Meat Beer Pizza Pasta Soda Juice Rabbitfoo
+d/;
$categories->set_has_tooltip(TRUE); # NOTE: thought this might help (n
+ope)
my $path = Gtk2::TreePath->new_from_indices(0);
my $tooltips = Gtk2::Tooltips->new;
#my $tip = Gtk2::Tooltip->new;
$tooltips->set_tip($categories,"tooltip test", $path);
$tooltips->enable;
my $window = Gtk2::Window->new;
$window->set_title ('SimpleList examples');
$window->signal_connect (delete_event => sub {Gtk2->main_quit; TRUE});
$window->set_default_size (800,600);
$window->add($categories);
$window->show_all;
Gtk2->main;