Why not just repot it and put it back outside? Another option would be to repot it and put it in a cold spot that would not make the plant succeptible to sprouting but allow the roots to develop. Unless you have an ideal way of providing enough light, I tend to shy away from keeping clematis from growing in the winter. The only exception to this rule would be if you are growing clematis from seed and some have germinated right now. I am in that situation and am using a shop light with regular fluorescent lights and the plants are doing just fine, but they are seedlings and not larger sized plants.

Another option would be to use duct tape to hold the pot together until spring and then replant it.

I have wintered over clematis in pots in my unheated garage. If the soil is frozen you could just put the pot and all in a bit bigger container and replant in the spring.