This can be accomplished by following 2 steps:

1. Add the following code in Editor > General > Design > Advanced > CSS styles field:

.gui_form .tabled_name { display:none !important; }

2. Add the following code in Editor > Pages > Registration form > Advanced > Javascript field:

<script type="text/javascript">
  $(document).ready(function() {
    $('#UserFirstName').val('Noname');
    $('#UserLastName').val('Nolastname');
  });
</script>

Note: This CSS code only works in "Classic" promotions (promotions that don't work with the Login). In promotions with the Login system, the "First name" and "Last name" fields can not be removed. Alternative: Use the "Alias" field and check the box to hide the First and ast name fields.