For FOSS you might set up a portal (SOAP XML/JSON/AJAX/
PHP/
Perl), a command limited console to run only certain zmprov commands, a java client, or even a zimlet to hide functionality in the admin console. (Probably don't want to do an admin console extension if these are different customer companies, as you'd be still marking accounts global admins rather than have ACLs to protect it, but might do the trick if the admins are trustworthy and just run different areas.)