Baby using as pacifier all night?

My daughter is 7 months old. From day one I would always get her to sleep by nursing her, and when she woke during the night, I would simply roll over (she sleeps with us) and nurse her back to sleep. This was fine when it was a few times a night, but the past month or perhaps longer, she wakes up all of time and cries until I put my in her mouth - and when I try to pull away after she falls asleep she starts crying again. Last night I felt like I didn't get a wink of sleep because of it. Are there any suggestions other than letting her cry herself back to sleep? The problem is that my 2.5 yr old can hear it from his room and wakes up crying as well if I let her go for more than a minute or two. She has also refused a regular pacifier from day one. Any opinions are appreciated!