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

my $response = $browser->post($url, [ %form_data ], @ns_headers);