What is the hardiness rating of your plant? I think most are marginally cold hardy to zone 6, but I am not sure about your miniature. Also potted plants are generally regarded as only being hardy to 2 zones warmer than they are listed because pots do not insulate the roots as well as the ground.

So, if your plant is hardy to zone 6, figure it is hardy to zone 8 in a pot. Find a place that meets those conditions and you are all set.

Sometimes keeping a plant in the dark forces 'deeper' dormancy than plants exposed to light and they can take greater coldness, but I wouldn't count on it unless you know the requirements of the plant well and I don't have any overwintering experience with your plant to say from experience.

Hi, I am in Z 8 and got one of those this year. Weeping Habit, purple flowers--really totally cool for pots!! the plant tag says it is hardy to 0 degrees. I have it in a big pot and am going to mulch it and put it against the wall of the house where I keep my hardy hibiscus and althea over the winter and I bet it does fine. However it gets a lot colder where you are--I sure do wish you luck--this is the only one I have ever seen of this type and I feel lucky to have found it.
Betsy