Here's a Delkin USB bridge device to connect two USB client devices together. Looks like it could be useful for an external hard drive?

http://www.buy.com/prod/Delkin_USB_Bridge_USB_File_Transfer_Device/q/loc/101/10370582.html

Edit: Never mind, I just read the fine print. This devices copies files from one device to another. Close, but not what I was looking for.

-Ed Coen