Can one have a mock return multiple messages (i.e. itself getting active having received a msg.)?

To test our application during development we have set up a couple of mocks to simulate several other systems that our's communicates with (using SOAP-requests).

Now, one of the other system always first responds with a technical acknowledge (essentially a response confirming that it has received and stored a message) followed - typically a few seconds later - by a sending a second, functional acknowledge message confirming that it now has validated and processed the previously received data. For certain processing our system has to wait for that second acknowledge, since it contains a new id given to the now processed data.

Can one mimik this behavior in a SOAP-UI  mock? Currently - while testing - we always have to mimic that behavior manually by picking the transaction-id from the first request and sending a "processed - confirmation" message to our system containing that same transaction-id. This is of course most cumbersome if one has to do this often.

I am sure one could automatize that using SOAP-UI, but how can I start a piece of code or a sequence in a mock?

Note: I know, how to setup a sequence processing responses and sending subsequent message when SOAP-UI starts the process, but in a mock it would need to be an incoming messages (incoming to the SOAP-UI mock) that would need to trigger such a sequence. I haven't found any description or example how to do that.

Any pointer or suggestion welcome!