AD Custom Attribute with unique value

view story

http://serverfault.com – I have custom AD attribute added to my AD schema. Attribute's syntax is Unicode String. It is added to user class and the purpose of it is to store user ID of corporate erp system. Problem is, that I can have two or more user objects with the same value stored in that attribute, which is something that I would like to avoid. Is there a way to configure AD attribute so it is unique within the domain boundary (same behavior as sAMAccountName attribute) ? i.e : If there already exists user object in AD with this attribute set to "JSmith" and I would try to set that attribute with the same valu (HowTos)