Unless you hack some files you have to use one siteaccess per language as the site.ini is the only way to tell ez which language to use and the site.ini allows only for one (main) language.
If you put the override settings in the general override directory they will be valid for <b>all</b> siteaccesses, including the admin siteaccess which is usually not desired. Therefore you really need a override.ini for each user siteaccess.
Using symlinks certainly sounds good, I haven't tried it yet. If that does not work I would write a small extension that copies the override.ini of the current siteaccess to all other siteaccesses. Then you just have to call up this script after you have made some changes to the ini file.
