Hey Tim,

Unfortunately it isn't possible to send all these data to the mail template but if you hack the model file in /administrator/components/com_easysocial/models/registration.php at line 806, you can push variables here,

[gist]
// Push arguments to template variables so users can use these arguments
$params = array(
'site' => $jConfig->getValue('sitename'),
'username' => $data['username'],
'password' => $data['password'],
'firstName' => !empty($data['first_name']) ? $data['first_name'] : '',
'middleName' => !empty($data['middle_name']) ? $data['middle_name'] : '',
'lastName' => !empty($data['last_name']) ? $data['last_name'] : '',
'name' => $user->getName(),
'avatar' => $user->getAvatar(SOCIAL_AVATAR_LARGE),
'profileLink' => $profileLink,
'email' => $user->email,
'activation' => FRoute::controller('registration' , array('external' => true , 'task' => 'activate' , 'activation' => $user->activation)),
'reject' => FRoute::controller('registration' , array('external' => true , 'task' => 'rejectUser' , 'id' => $user->id , 'key' => $key)),
'approve' => FRoute::controller('registration' , array('external' => true , 'task' => 'approveUser' , 'id' => $user->id , 'key' => $key)),
'manageAlerts' => false,
'profileType' => $profile->get('title')
);
[/gist]


For instance, if you want to pass the variable $hello into the e-mail template, you could do

[gist]
'hello' => $user->getFieldValue('SOME_CUSTOM_FIELD')
[/gist]