whats will kill your fish is lack of oxygen, the warmhanger the water the less O2 there is in it, co2 and o2 are exces at the waters surface... so the more you can get the water from the bottom of the tank circulating the more o2 you can get into the water, personaly id direct your filteroutlet along the surface of the water, thiss will move the water there along and down when it hits the other end of the aquarium and so pushing water at the bottom up so it can get o2.
leaving the lid off so warm water can escape as it evaporates will help, also a fan in the room blowing towards the tank will help.
as for the ice and frozen drinks bottles i`d only do that on a large tank, when you can be around all day, as the rapid temp change will stress your fish more and they are more likely to sucomb to illness