Profile2 regpath move account email field, into profile2 form and handle submit

I have a profile2 regpath displaying my profile2 form, and the system default account registration form below it. I need to move the account email field up into the container with the profile2 fields.

I have altered the form and moved the account mail field from the account form, into the profile form, and I have created an additional validation handler to try insert the mail value into the $form_state value so the user_account_form_validate() doesn't choke on a missing ['mail'] index:

function si_student_form_user_register_form_alter(&$form, &$form_state, $form_id) {  global $user;  // remove fieldgroups and tabs for anonymous users, e.g. /student/register  if($user->uid == 0) {    // move email field from account to below profile2 name fields    $email = $form['account']['mail'];    unset($form['account']['mail']);    // add email to profile    $form['profile_student']['mail'] = $email;    // change weights    $form['profile_student']['mail']['#weight'] = 3;    // custom validation handler to inject mail value into     // correct place in $form_state['values'] array    $form['#validate'][] = '_si_student_register_anonymous_validate';    //dpm($form);  }}function _si_student_register_anonymous_validate($form, &$form_state) {  $form_state['values']['mail'] = $form_state['values']['profile_student']['mail'];}

However this isn't working, and I get the following:

Any ideas? I'm not sure I'm taking the right approach here. Thanks