If you think that your blueberry plants are going to suffer from frozen roots in the pots, Urbanite, you could bury the whole pot in the ground up to the soil level on the stem and mulch the area over with straw or compost until the Spring, when you can plant them properly.
I add sulphur chips annually, a good handful per bush,usually in Spring (although this year I did it last week as I was weeding around them and just thought I would) and Blood, Fish & Bone in February. They are mulched with chipped up conifers which we get from local tree surgeons from time to time, as this is also slightly acidifying.