[Load balanced environment] Disable UI access in "tracking" server (no replies)

Hi all,
is it possible to set "maintenance_mode = 1" only in "tracking" webservers in a load balanced environment (x1 database, x2 tracking webservers, x1 UI webserver)?
I would like to maintain the access to web panel only in UI webserver, but in this FAQ is reported:

synchronize config/config.ini.php on all servers - make sure the file config/config.ini.php is the same on all servers (using rsync for example).

How can I solve this?

Thank you very much! ;)