How to fill hidden field with Capybara?

I've already found that when I want to set value to text field, text area or password field, I can use id, name or label as something in fill_in something, :with => some_value. However such approach fails when I try to set value to <input type="hidden"> field (and I want to do it because those are normally filled client-side scripts which I test separately). How could I set such a hidden field wit

[shoutatani]

jsでhiddenにアクセスしてみろって？お風呂入ってからやってみよう

[rightgo09]

Capybaraでhiddenフィールドに値を直接埋め込む方法