Hi - Let me start with please don't put something sour on your breast to stop him. Nursing has been a good experience for both of you and curbing it down slowly over a couple of weeks is the better way to go.
Has he dropped the morning nursing? If so start there at the beginning of the day. Go to the store and let him pick out a sippy cup that he likes. Make a BIG deal about it even let him pay for it himself giving the cup then the money to the clerk. Let him open it and wash it out with soap. Seems silly but the more connected you can get him to the cup the better.
Start with dropping the naptime nursing by putting a little milk in the sippy cup and letting him sip it in his crib. Only a little milk so he knows when it's empty it is time to sleep. Work thru the complaints with the cry it out technique. Hang in there for the first unhappy nap times then SMILE when it starts to work and it will.
Continue to give the NightBedtime nursing as your milk production decreases. Nurse a little then finish with the cup or vise versa which ever works for you. Again use the cry it our tech. after poutting him down for the night.
After two - three weeks your milk should be gone and the adjustment made by him to the sippy cup. Good Luck - God Bless