Refering to Baby Love by Robin Barker. She says giving baby formula cold is not at all harmful. I have given my 8 month old daughter cold formula on quite a few occasions when out and unable to heat it and she drinks it with no problems. Your son may even enjoy it being cold as you are in QLD and it is fairly hot. If you don't want to give it to him really cold, maybe just stand it in warm water to take the chill off, but not enough to warm it or if you wait for the kettle to cool down to room temperature, then make the bottle up with the room temperature water, so that its not really cold nor hot.
Julie, mum to Abby 05/02/04 & Joel 12/04/07