I have a USB HD plugged into an Airport Extreme in building #1 that is LAN connected to a Timecapsule (TC) in building #2 . I'd like to use the TC to back up the USB HD, but when I go into the TC options window the USB HD does not appear on the exclude list. I've read that the TC is capable of performing this function, but have not been able to find instructions on how to make it work with the airport extreme.