Do not cut it back, that's the worst thing you can do - if it gets caught and frosted, at least you've got some protection from the outer growth so that the central core of the plant might survive. Unless you can move it somewhere warmer, or are prepared to run in and out with horticultural fleece when the weather is severe and remove it when its not so bad, not a lot you can do. Remember to brush off accumulated snow so that the weight of it does not break the branches - a little snow is fine, insulates things.