Symfony 2.1 - Switch Monolog channel in controller

I want to log into a different file than the usual dev.log or prod.log

I know that this can be done with different channels and I used it in several services, but I'm not very clear about switching the Monolog channel in a controller.

In a service you just define the channel via the tags attribute in the service definition, but how can I do this in a controller or even better in a specific action?

I know that a possible solution would be this: Symfony 2 : Log into a specific file

But it seems overkill to define two new services just for logging to a custom file.