I've got a 1 gallon experimental blueberry ale in the secondary right now. I kept the beer in the primary for 8 days then racked onto 1lb of thawed (frozen) blueberries. I didn't watch closely but for at least the first 24 hours I had re-activated fermentation and had very slow activity in the airlock. I've kept the batch in the basement off the floor the entire time covered with a wool sweater. I don't know the exact temperature, just a bit warmer than average basement temperature. Perhaps after you add the fruit, you should have the hydrometer help you in deciding when to cold crash?
Keep us posted with what you decide to do.