[eluser]SneakyDave[/eluser]
the following method might be overkill if all of your restaurants are going to have the same function and use the same views, controllers, and databas, but its a pretty common setup.
What I've done in the past, is put the CI system folder outside of the root, such as if the restaurant.com's web root was:
/var/www/html/
I'd put the CI system folder in /var/www/
Then in /var/www/html/ you can have your "application" directories in there, named after the restauruant names
/var/www/html/joescrabs
/var/www/html/samsfish/
each of your restauruant folders is an "application" directory to CI, with its own configs, views, etc.
You will have to make adjustments in your application/config/config.php file to tell your app where CI is, and where your "application" folder is.