Some children on the spectrum seek sensory input when I work with them in art therapy. One client that I work with can not use tradition drawing materials for any focused amount of time. I have found that there are other ways to "draw" images that keep him engaged better.
Model magic is another material that can be used for picture making. I think I have showcased this before, but can not emphasize its usefulness. This child was able to manipulate the modeling material into shapes thius creating the whole image. As he "practices" with engaing materials, his drawing skills improve and traditional media can be introduced gradually.