Having multiple SSL certificates is a real pain. And it's quite slow! Don't do it -- tell the client that it costs too much
(if he asks HOW much, tell him at least 20 times what you'd ask for a "normal" one).
The only way the server have to know which site the user is trying to access is trying ALL the certificates (using the private keys). *UNLESS* your client accepts to have an explicit port number in the URL. Or you have access to a different IP for every SSL certificate and then redirect to the same virtual host.
I did it some years ago and wouldn't do it again.