I'd agree with Colin and David, it's not really necessary, as long as they get below about 12 degrees C.
If you do still want to hibernate them, a fridge is probably the safest place, but a frost-free shed, garage etc. would be fine. Don't feed them for at least a week beforehand, to empty the gut (so food doesn't rot inside them), and place them in a container with some damp moss or tissue paper. Check them every now and then to make sure they don't dry out.