I work with severe to profound MI as well. With your student, one way to make progress is to increase the criteria. For example, if responsiveness to, say, auditory stimuli is 40% then write the goal to increase it to 50%. On the other hand, are different cues needed? For example, would the student be more responsive to auditory stimuli, if he/she held the object (with hand over hand). The activities are limited, but there are ways to modify the goals so that you either change the criteria, cueing, or materials.
Hope this helps!