My mom started me on rice/oatmeal and vitamin D milk when I was 5 weeks old because I couldnt handle formula and she couldnt nurse (she didnt produce enough milk). This was under doctors orders. She said I went from being the crankiest baby to the happiest one she ever met.
I now have 3 kids and all of them started rice/oatmeal at 2 months, none of them did formula for more than a few weeks because they couldnt handle it. Even the expensive perscription $45 16 oz cans. I breast fed each of them until they decided they didnt want to anymore. Which was different for each one. Usually after going back to work and introducing the bottle.
I know in today's society the whole "6 months" is the earliest before food, but I survived, my cousins survived (also put on the same diet) and my children survived and we are all healthy. (My oldest is 13 and youngest 7 weeks).
Just start with 1/2 tsp into their milk for 2 weeks then add another 1/2 tsp for another 2 weeks. Then make 1/2 tsp with just enough milk to spoon feed it. This keeps from upsetting their stomachs. Start spoon feeding small, because they arent going to know how to do it. Dont get upset if they only take 3-4 bites then want the bottle, dont force them. Let them go at their own pace. Once they get the rice/oatmeal down, then add a little flavoring, such as a scoop of baby applesauce. When you think he/she is ready, introduce new foods. Just remember, small is key to not uspetting his/her belly.
I only recommend this if formula/breast feeding is not a good option. However, at night putting 1/2 tsp of oatmeal/rice in their bottle will help them sleep longer.
My son (7 weeks) went from eating every 2-3 hours to 4-5 hours. He's the only one that can handle formula. My husband and I call it the "nighttime special". He is only getting a scoop of rice in his nighttime bottles right now. We use a formula scoop, but only fill it 1/2 to 3/4. This was after doing the 1/2 tsp thing.