Conditionals of a User Role
I'd recommend using hook_form_alter and user_has_role in a custom module. It allows you to alter the form programmatically and perform logic in your hook function so you can access your user's role and modify your fields that way. For example, you could do something like:

function yourmodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id=='your_form') {
     global $user;
     if (user_has_role(your_rid)){
       // add the extra field you need here
     }
  }
}


there are many examples on how to modify/add fields in the hook docs link above, plus you can google more tutorials on that.