Last year I planted many clematis right before it snowed and didn't lose a single one. I did the same with a bunch of hosta and didn't lose any of those either.

I don't know why it worked out so well - maybe it was because they were dormant or almost dormant, maybe it was because we had a good snow cover most of winter without the freeze/thaw cycles that we typically experience. I did the same the year before and we had a lousy snow cover with many freeze/thaw cycles. I don't know, but as each season passes, I become more convinced that clematis are far more hardy than they were given credit for in the past.

I'm not recommending planting this way (how is that for a cop-out) but I'll probably do it again this year.

When I get small plants at the end of the planting year, I pot them up a size larger and sink the pots in the ground next to my south-facing foundation wall. When we have a thaw in the middle of winter or in early spring, I'll give the pots a drink because they're under our deck and no rain falls there. I have also overwintered clematis and small roses in my garage, but they tend to start growing a lot earlier than the outside pots, and are more trouble. Again, you have to give them some water every so often. I'm lazy enough that I like the less-work route.

I don't mind watering them in the garage but I know myself and I would probably overwater them. Maybe planting them in the pot would be the better option.