Cisco AAA/Identity/Nac :: Set Up ACS 5.3 Administrator Accounts To Authenticate?

Have set up a pair of ACS 5.3 servers and have set up device administration authentication be passed through to an RSA server via RADIUS. All works great.
 
What we want to do is go a step further and set the system up so that ACS Administrators also have to authenticate to the ACS system by RSA via RADIUS (the same as the Device Authentication we've set up) for ACS administration tasks.
 
Looking at the options available in the ACS Administration setup (administrator accounts etc) there doesn't seem to be an option to authenticate via another method apart from a local administrator account on the ACS.
 
Is it possible to do this?