Srdjan Vranac has a new post to his blog showing you how to create a custom repository with the dependency injection features that already come with the Symfony2 framework.
I am currently working on some Symfony2 bundles, I needed a custom repository to house hold my custom queries, that part is easy with sf2, and quite nicely explained in the Manual.
He walks you through the setup of a simple custom repository (a part of a Code4Hire bundle) and a (less elegant) call that can be used to reference it and its methods. To make things a big more clean and take advantage of the full dependency injection features of the framework, he makes a change to move the repository into the services.xml. This defines the container and makes it available to the application directly in function calls (like his render() example near the end of the post).