J.P.
Sorry, but the cereal doesn't make the baby sleep longer.
I would work on getting her to sleep through the night rather than trying to wean, if the waking up is the issue. Put her down later, let her cry it out, or other methods that you like, etc. At 8 months she should be big enough to sleep through the night (I think they say about 12 pounds). Waking up sounds more like a habit and comfort than a need.
If you do want to wean, you will still be waking up, and will either have to fix a bottle or pump. If you want her to take the bottle, have someone else give it a try when you aren't there. Many babies won't take a bottle from mom, if the breast is right there. They don't understand. Good luck.