Tracy suggests weaning the df gradually. For example, if you are currently feeding 6 oz. at 11 pm, move that to 5 oz. at 10:30 pm, and add one ounce to his first daytime bottle. Do that for 3 days. Then, drop the df bottle to 4 oz. at 10 pm, and add the dropped ounce to his second daytime bottle. Do that for 3 days. Then drop the df bottle to 3 oz at 9:30 pm, and add the dropped ounce to his afternoon bottle. Do that for 3 days. Then drop the df bottle to 2 oz. at 9 pm, and add the dropped ounce to his bedtime bottle. Do that for 3 days. Then you should be able to drop the 2 oz df entirely.
I did this with my ds, and it worked pretty well. I did do the 2 oz df for longer than 3 days, just because of my own paranoia that he would start waking in the middle of the night for feeds. But actually, once I completely dropped it, he slept better! And we've been df free for two months now.
Good luck!