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');
      }
   }