Hey Alison,
Ooohhh the Nuk. Everyone loves the Nuk. As a former preschool teacher I have taken many Nuks. I began to acquire a bit of a reputation at my preschool because somehow my room turned into the potty-training, sleeping on mats, giving up Nuks and time-out room. Not sure how I feel about that, ha! I was nice... but I had 3 year olds and I couldn't keep track of Nuks and bottles and kids jumping up off mats at naptime, etc....
Okay - so... Nuks. Here is what I've done for years, and it totally, totally works. Take it with a grain of salt as I obviously don't know you guys - but I've done this not only with my own, but with my preschool classes as well.
Over the course of about 10 days, cut his Nuks down with scissors. The first time, do just a teeny-tiny bit. Make sure you cut all of them down the same length every time, equally.
After a few days the nipple of the Nuks should be about half way gone. At the end of 8-10 days, there should be no nipple at all.
I simply explained that the Nuk was all gone.
Reactions - some kids would get frustrated, and talk about it for several days before being willing to throw it away. Some kids would cry. Some would be totally okay with it and collect all of the Nuks and toss them out themselves.
Your son's reaction will depend on his personality and also on your approach. Treat it the exact same way you'd treat an ice cream cone or another yummy treat - its gone! Uh-oh... all gone! And try to keep it very light and surface. After a moment to let it sink in.. move on quickly. Don't try to do anything. Find some toys with him or start a game... after a little while he'll bring it back to you asking what happened... and you just give the same response. After a while, he'll be alright with it. Maybe not at first - but after a while he will be fine.
Eventually you can throw them all away.
Its a much more pain-free way to do it than to just take them all at once, and it logical. He can't suck it if the nipple isn't there. And although he may carry the plastic piece around for a while... the mouth-fixation thing will die down and he'll move on.
Just a suggestion.
Good luck!