Is it possible in SoapUI to use a script to set the response of a test step?

I have a test step that sends a soap message to an ActiveMQ topic. My SUT gets the message from the topic, processes it and then sends the message to a detached mockService in SoapUI. I have these working. What I want to do now is make the test more automated by writing a script that when the mockService gets a message that inserts a response into the test step.

I am at the point where I can reach the test step from my script but I don't know how to populate the response.

Any help would be appreciated.

Thank you