Some women have had success with putting a bandage over their nipples and saying it's sore/booboo. It worked for me in that my son wouldn't ask for it but he would cry and cry at sleep time because it was how he'd fall asleep. It took me 2 weeks of not giving in to his cries (despite them breaking my heart into a million pieces) for him to be completely weaned. Before weaning i had him down to feeding for naps and at night only (but he'd wake 4-5 times a night).
Weaning was really hard but because I'm pregnant i needed to do it. After i weaned him he finally started sleeping through the night.
Anyway, other mums have also had success with rubbing something really yuck on their nipples like aloe vera etc.

All the best!