assuming that you may not have a cold basement, cellar or a beer cave, a laborious method would be to do put the entire carboy containing your premature beer in a cold water bath refilled with ice 2-3 times a day.
I did this for a week in summer a year ago, my primary was in a 5 gallon beer bucket, and I used a rubbermaid clothes storage container (plastic) filled with cold water. i used two 5 litre jugs of mineral water container and put that in the freezer for ice. And changed ice twice a day. As for the secondary, I had no option but to bottle all my beer and cold condition the bottles in my fridge.
Today, I have a secondary lagering on my balcony. Its 42F or 5.6C outside.
Good luck