The patron id gets stored as a user “meta data”, using the WP php function update_user_meta(). It should be possible to add elements to wp_usermeta, if you know *exactly* what you are doing.
Here is what things look like from mysql (from my test site):
mysql> describe wp_usermeta;
+------------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------------------+------+-----+---------+----------------+
| umeta_id | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| user_id | bigint(20) unsigned | NO | MUL | 0 | |
| meta_key | varchar(255) | YES | MUL | NULL | |
| meta_value | longtext | YES | | NULL | |
+------------+---------------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
mysql> select * from wp_usermeta where meta_key='PatronID';
+----------+---------+----------+------------+
| umeta_id | user_id | meta_key | meta_value |
+----------+---------+----------+------------+
| 36 | 1 | PatronID | 1 |
| 41 | 2 | PatronID | 100 |
+----------+---------+----------+------------+
2 rows in set (0.01 sec)
