Replace the orm:schema-tool:update command from Doctrine 2 with UpdateCommand.php. It will allow you to ignore table starting with B_ (see bootstrap file)

bootstrap

// Set this Doctrine 2 connection configuration to ignore view starting with B_

$config->setFilterSchemaAssetsExpression("/^B_/i");

RemoveFilteredTableEventSubscriber.php

<?php

namespace Comet\Event\Subscriber;

use Doctrine\Common\EventSubscriber;
use Doctrine\ORM\Tools\ToolEvents;
use Doctrine\ORM\Tools\Event\GenerateSchemaEventArgs;

class RemoveFilteredTableEventSubscriber implements EventSubscriber {

  private $filter_schema_assets_expression;

	public function __construct($filter_schema_assets_expression) {
		$this->filter_schema_assets_expression = $filter_schema_assets_expression;
	}

	public function postGenerateSchema(GenerateSchemaEventArgs $args) {
		$schema = $args->getSchema();
		
		$table_names = $schema->getTableNames();
		foreach ($table_names as $table_name) {
			$table_name = substr($table_name, strpos($table_name, '.') + 1);
			if (!preg_match($this->filter_schema_assets_expression, $table_name)) {
				$schema->dropTable($table_name);
			}
		}

	}

	public function getSubscribedEvents() {
		return array(ToolEvents::postGenerateSchema);
	}

}

UpdateCommand.php

<?php

namespace Comet\Command\SchemaTool;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Component\Console\Input\InputOption;

use Doctrine\ORM\Tools\SchemaTool;
use Doctrine\Common\Annotations\AnnotationReader;
use Doctrine\ORM\Tools\Console\Command\SchemaTool\UpdateCommand as DoctrineUpdateCommand;

/**
 * Command that overrides the orm:schema-tool:update to ignore tables
 *
 * This override will look for the annotation 
 * @Comet\Annotation\IgnoreSchemaUpdate in entity definition. If it's there,
 * the entity will not be added to the metadata to update
 */
class UpdateCommand extends DoctrineUpdateCommand {

  protected function executeSchemaCommand(InputInterface $input, OutputInterface $output, SchemaTool $schemaTool, array $metadatas) {
		$em_helper = $this->getHelper('em');
        /* @var $em \Doctrine\ORM\EntityManager */
        $em = $em_helper->getEntityManager();

        $event_manager = $em->getEventManager();
        $conn = $em->getConnection();

        if ($filter_expression = $conn->getConfiguration()->getFilterSchemaAssetsExpression()) {
        	$event_manager->addEventSubscriber(new \Comet\Event\Subscriber\RemoveFilteredTableEventSubscriber($filter_expression));
        }

		parent::executeSchemaCommand($input, $output, $schemaTool, $new_metadatas);
	}

}