you can purchase a cooling device for aquariums, or just keep their enclosure in a cold area. Some of my newts like it colder than 65F, so I keep them for a couple months in a cooler at 38-40F. This might work for yours, just don't use as much ice as I do, and the temp probably will not get too low, but still low enough.
You could also place the enclosure by a window or door that gets a draft of cold air.