Ssl – How many domains can be bound with one SSL certificate

You shouldn't need a second IP address or a second website. All you need to do is get a new certificate issued for your existing site, with the addition of the "Subject Alternate Name" attribute defined. This will you to use the same SSL cert for multiple fully qualified domain names.

In this case you would need separate ports if they were on the same IP, or separate IPs if you wanted them on the same standard SSL port (443). IIS doesn't support reading host headers and redirecting using SSL. You can use the same wildcard certificate without any issue, but you would need something inbetween IIS and the client (like Microsoft Forefront Threat Management Gateway) in order to do routing by hostname over SSL. (I hope that makes sense)

The reason this happens is because the connection is encrypted and the certificate is validated before the HTTP header is actually sent, so at that time IIS has to know what site it's using beforehand. Now, Firefox does send the hostname in with the initial encryption request but I'm not sure if IIS supports that (or if any other browsers do).

The First Few Milliseconds of a HTTPS Connection has an incredibly in depth description on how HTTPS generally works (through a special debug build of Firefox). As you can see a few paragraphs in TLS supports a server name extension, but as far as I know IIS does not support that extension.