[CAKEPHP] Customize add view - Change dropdownlist to radio buttons

I have a add.ctp... In the model I want to add I have a relation belongsTo, so when I generate that add view he creates a dropdownlist input.

But I want to use radiobuttons instead... I already have the code of the radio button and inside the view I can get wich one is selected.

My problem is, how I pass that value to the controler inside the $this->data array? Or should I just use $_POST inside the controler and do a savefield after the record is created?