my $object1 =  new MyClasses::Object1 (
                        _cgi   => new CGI,
                        param1 => '...',
                        param2 => '...',
                 );

  $object1->dothis;

  my $object2 = new MyClasses::Object2 (
                        _object1 => $object1,
                        param1   => '...',
                        param2   => '...'
                );

  $object2->setsomething;

  my $object3 = new MyClasses::Object3 (
                        _object1 => $object1
                );

  $object3->blah;

##</code><code>##

 Inside Object2:
   sub setsomething {
      my $self = shift;
      $self->{_object1}->{mode} = 1;
   }

 Inside Object3:
   sub blah {
      my $self = shift;
      if ($self->{_object1}->{mode}){
          return $self->{_object1}->{_cgi}->param('blah');
      } else {
          return $self->{_object1}->{_cgi}->param('pleh');
      }
   }