The field should have been added automagically to the Global Directory when you are editing a user. Since it obviously did not, try going to the Windows Services applet under Administrative tools, choose IIS Admin, and do a Restart. Say Yes when prompted.
When that is done, check again. If it's still not there, you will need to go into the DC Directory to update the field by hand that turns this field on, then restart IIS Admin again.
If you need help with this, please feel free to open a case with the Cisco TAC, but the field is in O=cisco.com/OU=CCN/OU=systemprofile/CN=System Profile and there is an attribute called "IAQ Flag" which should be set to "true". Or you can use your favorite command-line ldapmodify utility to do this.