Take a look at the treatments thread. In the "info for professionals" article, Sage wrote up a hierarchy. I'm using a variation of hers. Here it is.
1. drawing of a stickman, with a line coming out of his mouth
2. drawing of a stickman vomiting
3. looking at the stickman and pretending he's real
4. looking at the most common words for vomiting (I picked the top five and worked with those)
5. reading sentences and paragraphs that involve vomiting, going from not graphic to extremely graphic
6. listening to tapes of people coughing
7. listening to tapes of people gagging
8. looking at pictures
9. looking at pictures, pretending its me
10. videos
11. videos, pretending its me
12. going to amusement parks, bars, anywhere where vomit is likely to occur
13. working in a hospital or detox ward
Hope this helps. I should be finished with my hierarchy by the end of this year, although the timeline is subject to change.
Ultimately we know deeply that the other side of every fear is a freedom. - Marilyn Ferguson
Habituation always defeats fear. - Edmund Bourne