Hi,
By default Moodle can't do this or else you need to custamize the code.
Or else
You can develope an external webform application for adding users and make use of external database authentication .
And within the external webform application you can acheive all your requirements.
For the application design and for discussing .
Contact me at
SKYPE : RAJEEV27
gtalk : rsrajeev5@gmail.com
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Regards
Rajeev