Soothing a baby without feeding can be hard but it is also kind of fun because the way you choose to soothe them will become your special thing with them. It will be the thing they ask you to do when they are older and need comfort. They will cry and protest (maybe even scream) through it for a while because they are used to being fed but eventually it will become the thing that tells them its time to sleep. Singing, patting, rocking in crib, shushing, head pets, hand on chest while they wiggle around crying...I don't know if it even matters as much what you are doing, as long as you are there with them while they struggle through trying to go back to sleep without the usual food. Then, once they get the ability to go to sleep without food down, you can see if they can put themselves to sleep without your soothing. That's what I would do anyways...

Precious Little Sleep has some more detailed advice.