Couple of methods:
1) Use container fields containing the graphic you want. They can be calculated container fields, if you like, or just set them via script.
2) Use the Hide Object When feature in the Inspector to hide the slugs (never heard that before) when they shouldn't show up. Put one in every position with a different Hide calculation (as appropriate).
I would tend towards the second option, since it's less complicated, but if you wanted to make it more dynamic so you can update the graphic objects (like with different colors, for example), then the container fields may work better.
Option 2 is exactly what I was looking for! Very simple!
I had given the option of putting graphics in a container field some thought, but just wasn't ready to try it without seeking guidance first.