Currently, I'm using Tk::Notebook for this kind of thing, and I used this little hack to remove the tabs at the top of the notebook:

# at the top of the program, after loading Tk::Notebook

sub Tk::NoteBook::InitTabSize {
  my $nb = shift;
  $nb->{'pad-x1'} = 0;
  $nb->{'pad-x2'} = 0;
  $nb->{'pad-y1'} = 0;
  $nb->{'pad-y2'} = 0;
  $nb->{'minW'} = 0;
  $nb->{'minH'} = 0;
}
[download]

It's a pretty ugly hack, but it works like a charm. No multiple mainloops or anything like that needed, you just do $notebook->add() to add "screens" and $notebook->raise($name_of_screen) to raise the screen you want.