Just open up the scanner and lean the side of your face over it, and as the scanner moves, roll your head to the opposite side.
ENLARGE or it won't work
Here's a homemade stereogram picture. I had 2 pictures of my head, each slightly different. After taking the 1st picture, I moved the camera 3 or 4 inches to the side and took the second picture. When I put the 2 pictures side-by-side I had to test them to see which one belonged on the left and which on the right.
There are red dots over the centers of each of the pictures. If you can stand it, cross your eyes enough for the 2 dots to overlap, and my face will pop out in horrifying 3D.
This thing was just laying in the driveway!