I'm not sure about pluging in a HD directly, but you should be able to use a networked PC to do something similar, running perhaps over a wifi network.
I saw a review of the mini s which included advice to try Tweaks2K, which has a tweak to "show network" on your device. See full article:
http://www.short-media.com/review.php?r=308
I am now using Tweaks2k (
http://www.tweaks2k2.com/) and did tick the "show network" box. It is now appearing (I have memory, storage card and network in file explore), but the folder is empty. I haven't really looked into it though, so am guessing I need to configure either my PC, network, firewalls or something. Be cool if it work though.
Good luck!