How can I sync records when we create the user in AD first without knowing the UKG employee-number?

We create user in AD first, where we will assign the email address.

We do not know the UKG employee number when we create the user account.

We communicate the email address back to HR so that they know what email address to use in UKG.

How can I sync records when we create the user in AD first without knowing the employee-number?