[logback-user] Dynamic loggers?

My app needs to create log files on the fly and put them in their own directories. For example, suppose a user creates a new entity in our system named "foo". We want to create a new subdirectory, /logs/foo, and put foo-related events there. When the user is done with foo, we need to close the logger and release resources. How can I do this with logback? The difficulty is that we can't know in advance the name of the logger or the filename it needs to use, so we can't configure it in logback.xml. Also, it doesn't look like Logger has a close() method, so even if I write a custom Appender, I don't know how I'd notify it to shut down. I'd prefer to use generic slf4j in the application itself.