Fixed Rate Load test strategy

Hi,
I'm running SoapUI Pro 3.0.1. In my load test, I have a data source, test request  and a data source loop test step. Test request test step actually invokes an external web service. How can i ensure that the rate applies only to my test request test step and not to others?

If not possible, what way can I use to ensure a steady TPS for the requests that go out?

Thanks,