Symfony 2 YAML passing arrays
What you are searching for is not really about Yaml itself, but about the Yaml loader of the Dependency Injection container.
If you search docs about it, here are the ones for the old component (v1): http://components.symfony-project.org/dependency-injection/trunk/book/05-Service-Description
Symfony2 comes with a new component (based on the same principles). You can find the official docs here: http://symfony.com/doc/current/book/service_container.html#service-parameters
Concerning your problem, you cannot access to keys of DI parameters, you have to flatten then manually.
You could use a DI extension to fit your need, take example on some bundles like: https://github.com/symfony/AsseticBundle/blob/master/DependencyInjection/AsseticExtension.php#L54 (maybe not the best example).