[BORG_Sandman]

Or just make your own "esp_admin.cfg" in the same directory where the autoexec.cfg ist located with the settings Rebel mentioned above.

Then add "exec esp_admin.cfg" to your "autoexec.cfg".
This will execute the esp_admin.cfg on every server restart, adding your admins.
I prefer to split configs in several files to avoid long "standard-configs" like autoexec.cfg and serer.cfg

btw:
Is it possible to restrict the activation of the plugin only to "real" spectators?
Right now you can see the beams and boxes when you are "only dead", too.

Using Teamspeak, Ventrilo etc. at the same time could easily be abused by "bad" admins.
So, "esp_admin + Teamspeak = Wallhack for privileged users" ;)