Maybe try and turn the issue around. Don't try and "wean", rather think about encouraging Sam to do some of the things that will help him self-wean:
*eat lots of different foods, including calcium sources
*drink milk from a cup as well as milk from Mum
*find ways of comforting himself that aren't booby based
*have a drink and some food first and then booby
*find a different way of going to sleep (assuming that he feeds to sleep)
Would an acceptable compromise be the "don't offer, don't refuse" option - if he asks for a feed and still wants one once he has had some water then give it to him. This way he's setting his own pace - and he will slowly cut back.