Factory Girl create_list with trait and dynamic variable

I'm trying to create some extra records from a Factorygirl callback. It has to use one of the traits in that factory and it has to pass it a dynamic variable. I thought I could do something like this:

create_list(:some_factory, 5, :some_trait, dynamic_variable: 1)

But I get an undefined method `dynamic_variable=' on the ActiveRecord object