You can always use the all-powerful overrideredirect(1). It's only drawback is your on-top window will be on top on every virtual desktop. The following script uses just about every trick. :-) It shouldn't leak memory with constant use.

#!/usr/bin/perl
use Tk;

my $mw= MainWindow->new();

##################################################################
my $dialogdel = $mw->Toplevel(-bg=>'steelblue');
#my $dialogdel = MainWindow->new(-bg=>'steelblue');

  $dialogdel->overrideredirect(1);
  $dialogdel->geometry('200x100+600+100');
  $dialogdel->configure(-cursor => 'top_left_arrow');
  $dialogdel->Label(-text=>"Ready to delete $key_sel",
      -bg=>'pink',
      -fg=>'black',
       -width=>20)->pack(-side=>'top',-fill=>'x');

my $dlabel = $dialogdel->Label(-text=>"Confirm delete $key_sel?",
             -bg=>'yellow',
                 )->pack(-side=>'top');

$dialogdel->Button( -text => 'Delete',
             -bg=>'yellow',
             -activebackground=>'orange',
             -command => sub{print chr(07) })->pack;


$dialogdel->Button( -text => 'Cancel',
               -bg=>'red',
               -activebackground=>'plum',
               -command => sub{$dialogdel->grabRelease;
                               $dialogdel->withdraw;
                               }
                 )->pack(-side=>'right',-anchor=>'e');

$dialogdel->withdraw;
######################################################################
+#3

$mw->Button( -text => 'Delete',
          -bg=>'yellow',
          -activebackground=>'orange',
          -command => \&delete_key)->pack;

MainLoop;

sub delete_key{
  $dialogdel->deiconify;
  $dialogdel->focus;
  $dialogdel->grab;
}
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