No, you'd use the Enter Value script action with a blank value field; and yes, you'll have to do this with all 30 fields separately since there is no mass data entry capability in Personas 2.0 scripting.
If you would leave the screen containing your custom fields, navigate to a different screen and return to the previous screen, then the custom fields would be cleared out but if you stay on the same screen, then you'll have to clear them out with your script.