Yes you can do it by using Tacacs or Radius:
aaa new-model
aaa authentication login default group tacacs+ enable
aaa authorization exec default group tacacs+ none
You need to manually define all the commands for users in privilege level 7 using "privilege" commands.
For ex:
privilege interface level 7 shutdown
privilege configure level 7 interface
privilege exec level 7 conf t
privilege exec level 7 write memory
privilege exec level 7 reload
privilege exec level 7 show run
Then you need to configure Tacacs/Radius server to return privilege level 7:
http://www.cisco.com/en/US/tech/tk59/technologies_tech_note09186a008009465c.shtml
Zhenning