Designers are increasingly faced with the challenge of targeting multimodal applications, those that span heterogeneous devices and use multimodal input, but do not have tools to support them. We studied the early stage work practices of professional multimodal interaction designers. We noted the variety of different artifacts produced, such as design sketches and paper prototypes. Additionally, we observed Wizard of Oz techniques that are sometimes used to simulate an interactive application from these sketches. These studies have led to our development of a technique for interface designers to consider as they embark on creating multimodal applications.