+1 on trying a hub. I have successfully hooked up two external drives on my 922 though a non-powered hub BUT had problems with the first one I tried so don't give up if it doesn't work until you've tried a couple different models of hub.
Depending on what you are connecting a powered hub may not be necessary. External drives with their own power draw very little if any from the USB connection. So one drive and the USB network connector should be fine without a powered hub. Your milage may vary!
Dish doesn't recommend/support USB powered hard drives connected to the receiver, so that's one situation where a powered hub might make things work.