The approach I would recommend would be to inject your DI / IOC container into your repositories, and then you can inject whatever is needed into your model objects. The final parameter of ObjectMapper::create() allows you to add additional dependencies to your Repositories.

$orm = ObjectMapper::create($db, $dispatcher, ['MyNamespace\\DataObjects'], $cache , [$myContainer])

Then in your repository class setting the $objectDependencies property will then inject all instances of your data objects with the configured dependencies.

class MyRepository extends ObjectRepository {

public function __construct(Connection $db, EventDispatcherInterface $dispatcher, ObjectMapper $objectMapper, CacheProvider $cache, ContainerInteface $container) 
{
    parent::__construct($db, $dispatcher, $objectMapper, $cache);
    $this->objectDependencies = [$objectMapper, $container->get('myDependency')];
}
//...