hey there,
I did have success with my lo doing w2s for habitual night wakings at 4.5 months old. It took me 3 nights of doing it, but it worked. He always woke at 4:30am and I knew it wasn't from hunger as well. As long as it is the same time every night, I think that it definately works. I didn't know how much to wake him at first, so I asked in the chat room...and the consensus was to just stir your lo. I would just touch his lips and put my hand on his chest and he would stir but not wake, and settle back into a deep sleep in seconds.
good luck!
Candus