kyle, Last fall I stored 4 roots in a ziplock bag with a damp paper towel inside and kept that bag in the cripser drawer of the fridge and they did fine. I only had them a week before transplanting, so I can't guaruntee exactly how long they'll last like this. All four of the ones I transplanted came up this spring though. This was the first time I'd ever tried transplanting any seng. I just tranplanted a couple more to the same area. It's just a curiosity thing for me.
Something else that I am sure would work just fine (possibly for larger quantities) is to get you a clean 5 gal bucket, drill some holes in the bottom for drainage, and fill it with some woods/top soil or even just a decent potting soil mix.
Just layer the roots in the mix and keep it moist. If you have a cool basement you could store it in, or even outside on the northside of your house where it gets very little sun I am sure it would do just fine.
Just don't let it dry out and make sure it does not get soggy wet (drains well).
If it is extremely hot or cold outside then a cool basement would be a better bet. If it is fairly nice fall weather then I am sure outside/northside just about anywhere in deep shade it would be fine.
You would want to make sure that something like a mole could not get in to the roots.