Hi
This is not possible as per the threads I´ve seing here. But, If you can give it a try, you could and an AP as a client on the AAA server and then try to reach the AP using the AAA credentials. Considering that when Global Credential is in place, the WLC username and password is send to the AP as well, this can be true to AAA.
-If I helped you somehow, please, rate it as useful.-