Disable chunked encoding for mock REST web service

I am using SoapUI 5.0.0 and have created a mock REST web service. The response from the mock service is being sent with "Transfer-Encoding: chunked". If I explicitly set a "Content-Length" header, then the response is no longer set to chunked encoding, which is good. Hovever, could somebody tell me if there is a way to dynamically set the Content-Length based on the size of the reponse, rather than having to hard code it? I have tried changing the Chunking Threshold setting in the HTTP preferences to blank, -1, 0, 1 and 10000, but it doesn't seem to do anything.