How can I get fields from referenced entities into scope for "Product pricing rules"?

I ended up patching the registration module to add hook_registration_event_count_alter() and then wrote a small module that counts up all the registrations so I can have my price points AND limited seating.

/**
* Implementation of hook_registration_event_count_alter().
* This hook was added to registration/registration.module approx line 628.
* I'd love to claim credit, but I got the hook from mlsamuelson 
* http://drupal.org/node/1904412
* 
* One of the requirements of this site is to have multiple price points 
* available when registering for an event (e.g. General $15, Student $10, etc.).
* AND limit the number total number of seats (not simply a limit per price 
* point).
* 
* Due to the "Why can't I access my custom fields in Rules?" bug discussed at
* http://www.drupalcommerce.org/comment/6634 I was unable to use the Rules 
* module to adjust the prices based on the type of ticket being purchased.
*
* I was able to use this new hook and EntityFieldQuery to find all products
* that share the same registration type and sum up all of the registrations.
* Setting $count to that total has the effect of allowing us to have a 
* limited number of "seats" at an event and still offer differnt price points.
* 
* $count is the number of registrations from all products that share the same 
* registration type.
*/
function regtweaks_registration_event_count_alter (&$count, &$context) {
  // Ge the entity of the event we are acting on
  $entity_id = $context['entity_id'];
  $node = entity_load($context['entity_type'], array($context['entity_id']));
  $registration_type = $node[$entity_id]->field_event_registration['und'][0]['registration_type'];
  
  // Find all the entities that use the same registration type
  $query = new EntityFieldQuery();
  $query->entityCondition('entity_type', 'commerce_product', '=')
    ->fieldCondition('field_event_registration', 'registration_type', 
      $registration_type, '=')
    ->addMetaData('account', user_load(1));

  $result = $query->execute();

  if (isset($result['commerce_product'])) {
    $product_nids = array_keys($result['commerce_product']);
  }

  // Sum up all the registrations on all the entities that share
  // the same registration type
  $query = db_query("SELECT COUNT(registration_id) as 'registrations'
                       FROM registration
                      WHERE entity_id IN (:ids)", 
                      array(':ids' => $product_nids)
                   );  
  $result = $query->fetchAll();
  if (isset($result)) {
    $count = $result[0]->registrations;
  }
}

I did...and I don't remember the particulars. I do know that the registration, commerce_registration, and commerce_pricing_attributes modules didn't work together in a way that suited my needs. Sorry I don't have details for ya 8^(