Having just figured this out myself, I’d like to shed some light on exactly how to accomplish this.

Symfony 2 & Doctrine 2.1

_{Note: I use YML for config, so that’s what I’ll be showing.}

Instructions

1. Open up your bundle’s Resources/config/services.yml

2. Define a table prefix parameter:
   
   _{Be sure to change mybundle and myprefix_}

   parameters:
       mybundle.db.table_prefix: myprefix_
   

3. Add a new service:

   services:
       mybundle.tblprefix_subscriber:
           class: MyBundle\Subscriber\TablePrefixSubscriber
           arguments: [%mybundle.db.table_prefix%]
           tags:
               - { name: doctrine.event_subscriber }
   

4. Create MyBundle\Subscriber\TablePrefixSubscriber.php

   <?php
   namespace MyBundle\Subscriber;
   
   use Doctrine\ORM\Event\LoadClassMetadataEventArgs;
   
   class TablePrefixSubscriber implements \Doctrine\Common\EventSubscriber
   {
       protected $prefix = '';
   
       public function __construct($prefix)
       {
           $this->prefix = (string) $prefix;
       }
   
       public function getSubscribedEvents()
       {
           return array('loadClassMetadata');
       }
   
       public function loadClassMetadata(LoadClassMetadataEventArgs $args)
       {
           $classMetadata = $args->getClassMetadata();
           if ($classMetadata->isInheritanceTypeSingleTable() && !$classMetadata->isRootEntity()) {
               // if we are in an inheritance hierarchy, only apply this once
               return;
           }
   
           $classMetadata->setTableName($this->prefix . $classMetadata->getTableName());
   
           foreach ($classMetadata->getAssociationMappings() as $fieldName => $mapping) {
               if ($mapping['type'] == \Doctrine\ORM\Mapping\ClassMetadataInfo::MANY_TO_MANY 
                       && array_key_exists('name', $classMetadata->associationMappings[$fieldName]['joinTable']) ) {     // Check if "joinTable" exists, it can be null if this field is the reverse side of a ManyToMany relationship
                   $mappedTableName = $classMetadata->associationMappings[$fieldName]['joinTable']['name'];
                   $classMetadata->associationMappings[$fieldName]['joinTable']['name'] = $this->prefix . $mappedTableName;
               }
           }
       }       
   }
   

5. Optional step for postgres users: do something similary for sequences

6. Enjoy