How about a "/images" directory that includes a .vuh file that grabs the image from the right (in-a-package) place? Your cache box would see a simple URL and be tricked into doing the right thing after the image was first delivered. This isn't much different than putting out trick URLs that Akamai understands (which I got to do for Greenpeace, fun!)
In other words ... in your environment you can hack code to do what you need even if the files are placed in a more package-friendly place.
