J.S.
My daughter is 17 months and like the other mother that responded, I still give her milk before bed as part of her nightly routine. I usually do so after her bath and then we brush her teeth just before bed. I think as long as you begin to establish a routine it will be fine. It may be hard the first few nights as changes in routine usually are but as long as you stick with the new routine it should be fine. My daughter drinks her milk in a sip cup, as long as your son is physically able to use the sip cup, which you said he is and uses it for water and juice, then milk shouldn't be a problem in it. He might not like it at first but if he is only getting milk that way he will eventually give in as long as you hold firm. Just remember that at one year children only need 16-24 oz of whole milk per day, I know it was hard for me to get my daughter use to drinking other liquids throughout the day at first but she got use to it after a while.