May be you can explain him that SEP 11 has reached EOL, there is no point in implimenting it in on such a large scale when you cant get support for it
http://www.symantec.com/business/support/index?page=content&id=TECH211491
You can install SEPM on all three sites and they can talk to DB, replication method
This discussion has all the necessary points, it might take some time to decide but worth reading
https://www-secure.symantec.com/connect/forums/designing-sepm-80000-clients-multi-site-deployment