Choices Callback + Parent Option gets removed from by validation.

Using hook um_before_save_filter_submitted or um_before_save_registration_details has wrong $submitted values due to I believe validate_fields_values()

In more details I have used a plugin that give user groups and I use the groups structure to populated two select form. This is a simplified form structure I have:

'company' => array (
  'type' => 'select',
  'metakey' => 'company',
  'title' => 'Company',
  'custom_dropdown_options_source' => 'getCompanies',
),
'sub_company' => array (
  'type' => 'select',
  'metakey' => 'sub_company',
  'title' => 'Sub Company',
  'custom_dropdown_options_source' => 'getSubsidies',
  'parent_dropdown_relationship' => 'company',
),

Code to fill the selects:

function termsToArray($terms) {
  $output = array();
  foreach ($terms as $term) {
    $output[$term->term_id] =
        html_entity_decode($term->name);
  }
  return $output;
}

// Function to extract main Companies
function getCompanies() {
  $terms = get_terms( 'user-group', array(
    'hide_empty' => false,
    'orderby' => 'term_order',
    'order' => 'ASC',
    'parent' => 0
  ));
  return termsToArray($terms);
}

// Function to extract Subsidies for a given Companie
function getSubsidies() {
  $parent_id = $_POST['parent_option'];
  $parent_term = get_term($parent_id, 'user-group');
  $terms = get_terms( 'user-group', array(
    'hide_empty' => false,
    'orderby' => 'term_order',
    'order' => 'ASC',
    'parent' => $parent_id
  ));
  $terms = array_merge(array($parent_term), $terms);
  return termsToArray($terms);
}

This part works nice. Data gets submitted, values come back as term ids. But when validate_fields_values() gets called on hook um_before_save_filter_submitted there is no way for the custom function getSubsidies() to respond without a $_POST and sub_company gets removed from $submitted values.

Now this creates multiple problems for me.
1. {submitted_registration} will always print “Sub Company: (empty)”
2. Will need to convert term_id to name for {submitted_registration} and I haven’t found a hook for that yet.
3. I needed to assign a user-group term to each new user. I was only able to do this because on um_before_save_filter_submitted I got the full $form_submitted_data.