member_member_register hook and Custom Member Fields

I am writing an extension that uses the ‘member_member_register’ hook to process the registrants the data array accessible from this hook seems to contain only the following key/values.

[group_id] => 6
    [username] => test
    [password] => 12312
    [ip_address] => 123.123.
    [unique_id] => 132
    [join_date] => 1294244703
    [email] => [email protected]
    [screen_name] => test
    [url] => http://test.com
    [location] => 
    [language] => english
    [time_format] => us
    [timezone] => UTC
    [daylight_savings] => n

I would like to process custom member fields completed on registration.

Any idea how I can access this data when extension is referenced by the hook?

I may try to find and query the table storing the custom member field using the member_id but would be interested to know of another approach to this.

Thanks,

Jack