CruiseControl.net, msbuild, /p:OutputPath and CCNetArtifactDirectory

I'm trying to setup CruiseControl.net at the moment. So far it works nice, but I have a Problem with the MSBuild Task.

According to the Documentation, it passes CCNetArtifactDirectory to MSBuild. But how do I use it?

I tried this:

<buildArgs>
   /noconsolelogger /p:OutputPath=$(CCNetArtifactDirectory)\test
</buildArgs>

But that does not work. In fact, it kills the service with this error:

ThoughtWorks.CruiseControl.Core.Config.Preprocessor.EvaluationException: Reference to unknown symbol CCNetArtifactDirectory

Documentation is rather sparse, and google und mainly offers modifying the .sln Project file, which is what I want to avoid in order to be able to manually build this project later - I would really prefer /p:OutputPath.