Is there some way to trigger adding a specific product to an open cart?

[lat9]

Note, too, that the example should be updated to show the use of the __construct function (that's going to be needed for PHP 7.0 compliance), e.g. changing references like:

<?php
 class myObserver extends base {
   function myObserver() {
     $this->attach($this, array('NOTIFIER_CART_ADD_CART_END'));
   }
...
 }

to

<?php
 class myObserver extends base {
   function __construct() {
     $this->attach($this, array('NOTIFIER_CART_ADD_CART_END'));
   }
...
 }