You can have all the USB drives connected to a USB fan-in. Then plug the power supplies into an individually switch power strip (I assume such should be available) and switch on only one at a time.
I do it by powering all the supplies (wasteful) and then like a switchboard, plug in one of the USB cables into the front of my DVR, actually I have 2 722s so I can be transferring up to 2 programs at once. This would mess up the USB fan-in. It's a little messy but with 5 WD 750GB and 3 various 1000GB drives you have to do something. I mark them with different colors dots and rubber bands or the cables themselves. All of this is plugged into a UPS along with the TV--turn the TV off soon if the power fails. No additional purchases needed but I do have to get up to switch them, oh so lazy.
Oh, all the programs are listed in an Excel-like sheet with sections for each disk and for each recording: HD/SD, IMDB-250 rank, IMDb rating, Dish name, IMDb name (if different), year, Dish rating, minutes, director and actors, recording date, MegaBytes, MB/hr, and channel name. Other sheets have 7 series recordings and the recent IMDb 250 listings to lookup for the main sheet. 1100 films and a couple of 100s of series.
-Ken