Hi A.,
I breast fed my daughter until she was almost three. During the last year or so, it was mostly just a comfort for her (like you said, a pacifier), and it was sort of nice in that it was a special bond that we had. Towards the end, I was totally ready to quit, but I didn't intend to press the issue. When she was almost three, I went away for several days, and she stayed with my parents. My daughter tried to nurse the day I got back, and she said it tasted "yucky". Whenever she tried to nurse after that, I reminded her that it didn't taste good, and I offered her something yummy instead. It ended up being a painless transition for both of us.
I know not everyone has the luxury of being able to get away for a few days, and I'm not even sure that everyone's breast milk flavor would change after a short time (maybe my daughter just didn't remember what it tasted like?). But maybe there's some food that you could eat or a supplement you could take that would change the flavor to something mildly unpleasant...
Good luck! :) I. :)