WCF Chunking / Streaming

I'm using WCF and want to upload a large file from the client to the server. I have investigated and decided to follow the chunking approach outlined at http://msdn.microsoft.com/en-us/library/aa717050.aspx

However, this approach (just like streaming) restricts the contract to limited method signitures:

[OperationContract(IsOneWay=true)]
[ChunkingBehavior(ChunkingAppliesTo.InMessage)]
void UploadStream(Stream stream);

The sample uses the rather convenient example of uploading a file from a fixed path and saving it to a fixed path on the server. Therefore, my question is how do I pass additional parameters to specify things like filename, filepath etc.

eg. I would like something like:

[OperationContract(IsOneWay=true)]
[ChunkingBehavior(ChunkingAppliesTo.InMessage)]
void UploadStream(Stream stream, String filePath);

Thanks in advance, Mark.