Hi there
IMHO, I would stop adding cereal to his bottle. Here in Canada they strongly discourage it as it is a choking hazard. If eating from a spoon is making him spit up, then I would try offering less cereal per sitting, making it runnier, or not offering cereal at all. Cereals are actually very hard to digest, and rice cereal especially can cause gas and constipation. The only reason that rice cereal is a recommended first food is that babies are almost never allergic to it and it's fortified with iron. However, if your lo is drinking his formula well he's getting plenty of iron from it.
In BWSAYP Tracy actually recommends starting with pears, as they are nutritious, easy to digest, and not very allergenic. Honestly, in your shoes, I would stop the cereal in the bottle, continue offering the cereal in the evenings if it's not causing you any troubles, and then offer pears at breakfast time in a couple weeks when he might be more ready for them. You should always offer new foods in the mornings so that you have the whole day to watch for an allergic reaction
what do you think?