Push value into array using form
You could try creating a session variable. Taken from this question

You can try this.

function lists_session($key, $value = NULL) {
static $storage;
if ($value) {
$storage[$key] = $value ;
$_SESSION['lists'][$key] = $value ;   // I use 'lists' in case some other module uses 'type' in $_SESSION
}
else if (empty($storage[$key]) &amp;&amp; isset($_SESSION['lists'][$key])) {
$storage[$key] = $_SESSION['lists'][$key];
}
return $storage[$key];
}


So, to save a variable in Session:

lists_session("s_key", "value");


And to retrieve the value, just use:

$myVar = lists_session("s_key");


EDIT

To attach the above to the form submit (Add), try the following, taken from this question. You can do this in template.php with THEMENAME_form_alter if you prefer not to create a new module, but it would be theme specific if you do that.

You will need to create a custom module with hook_form_alter() implementation.

function [YOUR_MODULE]_form_alter(&amp;$form, &amp;$form_state, $form_id)
{
  if($form_id == "YOUR_FORM_ID")
  {
    // target the submit button and add a new submission callback routine to the form
    $form['#submit'][] = 'YOUR_SUBMISSION_CALLBACK_FUNCTION';
  }
}


The code above will execute your new callback function YOUR_SUBMISSION_CALLBACK_FUNCTION AFTER the form's default callback function.

To make your new callback function called BEFORE the form's default callback function, use the following code instead of the giving above:

array_unshift($form['#submit'], 'YOUR_SUBMISSION_CALLBACK_FUNCTION');


To cancel the form's default callback function and force it to use your function ONLY, use the code below

$form['#submit'] = array('YOUR_SUBMISSION_CALLBACK_FUNCTION');