从我在这里找到的内容启发，我想到了使用javascript在隐藏对象textarea和CKEditor对象上设置数据的解决方案。视情况而定，两者似乎都不足够。

def fill_in_ckeditor(locator, opts)
  content = opts.fetch(:with).to_json # convert to a safe javascript string
  page.execute_script <<-SCRIPT
    CKEDITOR.instances['#{locator}'].setData(#{content});
    $('textarea##{locator}').text(#{content});
  SCRIPT
end

# Example:
fill_in_ckeditor 'email_body', :with => 'This is my message!'