my @form_data_pairs = (
  'Encounter1847760942'           => $enc_id,
  'SelectType1847760942'          => 'StartOnSelect',
  'Begin1847760942'               => '01/02/2005',
  'DaysBack1847760942'            => '3',
  'ProcedureSearchText1847760942' => '',
  'EncounterOptionSelected'       => 'false',
);
# ... Code to handle dynamic options would go here ...
my $cb = ($some_dynamic_flag) ? 1 : 0;
push @form_data_pairs, (
  'checkbox' => $cb,
  'something' => 'Something else',
);
push @form_data_pairs, ('checkbox2' => 1) if $some_other_flag;

my $response = $browser->post($url, \@form_data_pairs, @ns_headers);