Back in my packing house days we worked in a refrigerated room that was 42 degrees F. The ladies boning loins on the line would get cold . So to shut the chillers off, we would put a few cubes of dry ice in a plastic bag and set the bag on the stainless steel box with a lock on it, that covered the thermostats. The chillers would shut off and it would start to warm up. When discovered, the federal meat inspector would slap the ice bag off the box and into the floor and go looking for the foreman. So in your case, a few ice cubes in a washcloth, and putting them on the thermostat, would do the trick.
My wife taught in an old elementary school and had a classroom on the NW corner of the school. She would wrap the thermostat in a wet paper towel, put a little fan on it and the thermostat would cool down, opening the valve for hot water to push through the radiators, This was a Herman Miller system. I had one in a school converted to a recreation center too.
Remember the old Desert Water Bag slogan “Cools by evaporation”!!!
Where there is a will there’s a way.
Strike while the iron is hot. Live every day as if it were your last and one day you will be right.