Ruby - How to remove a setter on an object

Given a class like this:

class B
    class << self
        attr_accessor :var
    end
end

Suppose I can't modify the original source code of class B. How might I go about removing the setter on the class variable var? I've tried using something like B.send("unset_method", "var="), but that doesn't work (nor does remove_method, or overwriting that method with a var= method that doesn't do anything). Any ideas?

class <<B ; remove_method :var= ; end