I have just been made aware of a product that will provide a relatively clean (average <1mV noise) 5V external supply on the USB cable. It is a linear 5V/1A external PS that links into a USB cable ( http://www.aqvox.de/usb-power_en.html). On the purchase page (http://www.aqvox.de/bestellung.html) they even state that it is suitable for the Hiface - maybe been looking in on the modifications mentioned here. Cost is €89 + shipping.
An owner of a MK1 (just emailed this to me about the AQVX supply above (reprinted with his permission):
An even cheaper ($30) & possibly cleaner option (40uV noise) is to be found here but it is a kit I think & may require some soldering?
Looks like these powered hubs will also work & are cheaper again ($14) but you need to provide a 5V PS http://www.newegg.com/Product/Product.aspx?Item=N82E16817731002 http://www.newegg.com/Product/Product.aspx?Item=N82E16817402014
Or this one which seems to be the cheapest yet ($3) http://www.streakwave.com/Itemdesc.asp?ic=5VUSB Again supply your own 5V supply