Gonzalo Ayuso has written up a new post about a handling method he's worked up for working with multiple PDO instances (database connections) through the Symfony2 dependency injection container using custom YML definitions and a simple "Db" class.

I’m not a big fan of ORMs, especially in PHP world when all dies at the end of each request. Plain SQL is easy to understand and very powerful. Anyway in PHP we have Doctrine. Doctrine is a amazing project, probably (with permission of Symfony2) the most advanced PHP project, but I normally prefer to work with SQL instead of Doctrine. [...] Due to my daily work I need to connect to different databases (not only one) in my applications.

He shows the normal setup using the "parameters.yml" file to define the multiple database connections but notes that this isn't the most ideal solution. Instead, he walks you through the steps to create the "databases.yml" configuration file and a simple "Db" class that acts as an interface to pull the PDO objects from the container. You can then just call the "get" method on the container to extract the fully configured PDO object, ready for use.