I agree that cold turkey is the best way, even though it will be difficult. I nannied for a few families in college, and one thing that helped some of my charges was when their pacifiers (or the infant feeder in your son's case) "went" somewhere... One little boy named Jack lost his because the family dog got one of his pacifiers, and he was SO upset, but he understood that Bear (the dog) ate it. His parents threw out all the other pacifiers in the house, and Jack was just done with it.
Another thing I have heard of doing (don't remember where, maybe even on here?) is throwing a sort of "ceremony" to rid of the security item...the story I heard was that a little girl needed to give up her pacifier, so they hung them all on the tree in the front yard at night. Then, a "pacifier fairy" would come down and gather all the pacifiers, and give them to the new babies!
Sometimes, in exchange for the pacifiers, the fairy would leave a present thanking the child for the pacifer...could be small or large
Either way, it's still cold turkey, but it might help him understand at least WHY the feeder's not coming back. Good luck!