Hi,
As per my knowledge it is not possible because Lobby Admin try to access the WLC as management user, that is why someone needs to tell the WLC what privilege does that user account will have.
I think this is only can be done RADIUS server.
http://www.cisco.com/c/en/us/support/docs/wireless-mobility/wlan-security/97073-auth-lobbyadmin-radius.html
Regards
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