The form helper isn’t really flexible enough to allow for any kind of structure, but you could create your own form templates as described here:
http://book.cakephp.org/3.0/en/views/helpers/form.html#customizing-the-templates-formhelper-uses
However, this is only sensible if you really plan on using these new structures all the time in your project. If it’s a one time thing, it makes more sense to just use HTML and fill it with the appropriate variables or create a helper.