Go to an automotive swap-meet and get a "cool can" its a metal canister that has a spiral of tubing inside. Racers put dry-ice in the canister, and pump fuel through the spiral. This gets the fuel nice and cool for those hot days at the drag-strip.
You should be able to use one(look for one with insolation in the walls of the canister) to cool anti-freeze in the same way. Then all you need is a watercooling kit. I've acctually wanted to do this for sometime, but I can't get dry-ice locally without a special chemical permit.