Programmatically assign user to domain and/or with Rules

I have also Domain Rules enabled - and am trying to get rules to assign the user to a (sub)domain as can be done on the "People" page manually (new.domain.com)

I have tried logging the user on during checkout via One Rule with

$account = array('uid' => $account->uid);
user_login_submit(array(), $account);

And then in rules using "set domain to user"

<?echo $domain ?>

to assign the user to the subdomain.

It does not work - and all else works to create the domain.

Is there some php code I can run to programmatically get this done after creating the subdomain ?? Looking through the documentation i can not tell between the domain user module (now gone) how this is done programmatically now