Add a text Autocomplete Widget programmatically

Trying to include a text Autocomplete Widget in a compound field (more here) using the snipped below.. but the field does not autocomplete. What am I doing wrong?

  $element['contact_name'] = array(
    '#title' => t('Name'),
    '#type' => 'textfield',
    '#default_value' => $defaults['contact_name'],
    '#weight' => 2,
    '#size' => '100',
    '#max_length' => '255',
    '#widget_type' => 'autocomplete_widgets_flddata',
    '#autocomplete_match' => 'contains',
    '#autocomplete_case' => '0',
    '#widget_module' => 'autocomplete_widgets',
  );