My first thought is Are you sure baby has been extra hungry all this time?
Sometimes babies can have what seem to be hunger signs and take more bottle when they are not hungry at all but suffer from some other ailment. Like tummy trouble, reflux, gas, teething. Sucking on a breast or bottle is also a comfort to them. Is he a fussy baby? And the bottle seems to quieten him? Check out the link below on reflux. The fact that he likes a 'thickened' feed is a classic reflux sign. It soothes his throat.
So I'm wondering if he ever needed the cereal in his bottle in the first place. Especially if you think he's getting bigger and hungrier. Plus--I have to add--and please don't be upset with me, this is just as much for other moms--it's considered dangerous and outdated advice to add any kind of cereal or food to a bottle. It poses a choking hazard. Plus no matter what you add, it still won't be as nutritious as the formula or breastmilk already in the bottle so you are kinda taking away nutrition yet adding bulk.
Bottle Feeding Tips from Dr. Sears
http://www.askdrsears.com/html/0/T000100.asp
Reflux in Babies
http://www.askdrsears.com/html/10/t106000.asp
Here's an excerpt from the previous link:
Signs that your baby is being fed too much at each feeding are:
* a lot of spitting up or profuse vomiting immediately after the feeding
* colicky abdominal pain (baby draws his legs up onto a tense abdomen) immediately after feeding
* excessive weight gain
Best wishes to you and the little one. And it's true, babies come in all shapes and sizes. I hope your sweet baby continues to be healthy!