Hi K.,
My youngest son absolutely LOVED his pacificer!!!! I know exactly how difficult this can be for you and your son.
First of all, I don't believe there should be "time limit" with a security need like this, so my opinion may not matter to you knowing that :O) But look at young kids who suck their thumb, or have a blankie.....they don't have to "give them up" at 2 yrs old. So, why should a pacifier kid?
I began when my son was 2-2 1/2, by giving him a gold box to put by his bed. He decorated it by drawing on it. I told him that was his Pacifier Treasure Box to hold all of his pacifiers in during the day when he was not using them. Pacifiers are only for sleeping and resting, I told him. So, everytime he wanted one, I said, "Of course you can have your pacifier now, that means you are sleepy, so you need to go lay on your bed until you are done resting". He would do it, and sometimes he would fall asleep, and other times he was only in there for about 15 mins. If he ever came out with his pacifier in his mouth, I just reminded him to go put it in his Treasure Box.
The first couple of times were the hardest because at 2yrs old they are still a baby at heart. We did that routine for about 10 months-12 months, until he was 3 and started Pre-school. Everyday after preschool he would go in his room by himself to have his pacifier for about an hour. That was a huge rest period each day for him.
About 2 months after he started Pre-school, he became "too busy to remember" his pacifier. My job was to keep them out of sight-out of mind. There were days he asked if he could go in his room, then there were days that he just wanted/needed it for bedtime. All of those reasons were completely OK with me.
One day, he realized it had been 5 days without his pacifier. And weined himself, in my opinion. I was NEVER the "bad guy".
About 6 months after that, he came across his Treasure Box and asked me what to do with them (his precious pacifiers). He wanted to give to my sister who had just had a new son :O) I called my sister and "prepped" her for the beautiful gifts he had wrapped himself for her. Thankfully, my sister "played along" with him because she knew he so generously gave up one of the most important things in his life. Then, there was closure forever!
This worked for me, and I feel very good (as a mom) that my son never thought I was "mean" about his pacifier.
I know there is talk about a pacifier ruining a childs teeth, but my feeling is that they are baby teeth, and a child is most likely to have had an issue with his teeth anyway. For the record, my son didn't have dental problems. He is just now loosing his front teeth in 1st grade :O)
I hope my experience helps guide you in the direction you want to go with this. I know how hard it can be to take something away from our children when they completely depend on them.
Good Luck!
~N. :o)