function example_theme() {
  return array(
    'deductible_form'  => array(
      'arguments'      => array('form' => NULL),
      'template'       => 'example',
      'render element' => 'form',
     ),
  );
}

function deductible_form($form, &$form_state, $var1, $var2) {
  $form['#theme'] = 'deductible_form';
  $form['#var1'] = $var1;
  $form['#var2'] = $var2;

  // etc...

  return $form;
}

function theme_deductible_form($vars) {
  $form = $vars['form'];

  $var1 = $form['#var1'];
  $var2 = $form['#var2'];

  // Render the form
}

$form = drupal_get_form('deductible_form', $var1, $var2);