gistfile1.php

<?php


my_module_FORM_ID_alter(&$form) {

  //Add a custom button
  $form['my_button'] = array(
    '#type' => 'button', 
    '#value' => t('My Buttom'),
    '#executes_submit_callback' => TRUE,
  );

  //Add a custom submit handler
  $form['#submit'][] = 'my_module_custom_submit_handler';

}

function my_module_custom_submit_handler($form, &$form_state) {

  //Add a special redirect for users who clicked 'my_button'
  if ($form_state['clicked_button']['#value'] === 'my_button') {
    $form_state['redirect'] = 'path/to/my/special/redirect';
  }

}