Well that's a bummer. Hacky possible solution: create a dummy campaign and add 0 leads to it then just use "not in" .
However, hopefully someone who has experience with this will answer but that's all I got.
Sheila Madrigal, I did my set up but it's nothing scalable. I work in a smaller org with more lead time between content projects that require me to update my operational campaigns, so I'm basically updating with the new campaign name each time. I don't recommend it.