Preparing Rice Cereal

My daughter, Karolyn, just went to get her 4 month shot today. Her adjusted age is really 2 months since she was born early. The ped said to add rice cereal to thickened her feeding since she vomits almost everyday. He said to add 1 tablespoon to 2 ounce of formula. Currently, Karolyn is being fed 4 ounces every 3 – 4 hours. Before, we prepare her bottles in advance for one day and store it in the fridge. Can we still do that w/the rice cereal? Can we add the rice cereal to the formula for each bottle and store it in the fridge or do you think we need to add the formula instantly everytime we warm up the milk? Thanks! Also does it really help w/the vomitting?