So for quite a few months I was pretty sure having HTTPS on multiple domains with the same IP was a no-go on nginx. I was wrong.

If you have a OpenSSL version >= 0.9.8f with SNI support compiled in and a half-way recent nginx version you are good to go. Just set up as many virtual domains as needed.

Quick example from memory (I'm quite positive it is correct though):

server {
  server_name somedomain.example.com;
  listen 443;

  keepalive_timeout 70;
  ssl on;
  ssl_protocols SSLv3;
  ssl_certificate /some/file.pem;
  ssl_certificate_key /some/file.key;
}
server {
  server_name someotherdomain.example.com;
  listen 443;

  keepalive_timeout 70;
  ssl on;
  ssl_protocols SSLv3;
  ssl_certificate /some/other/file.pem;
  ssl_certificate_key /some/other/file.key;
}
server {
  server_name evenotherdomain.example.com;
}

Keep in mind though, that enabling SSL in any way leads to a kind of catch-all situation. Meaning if you access https://evenotherdomain.exmaple.com you will most likely end up on one of your SSL-enabled domains (domedomain.example.com or someotherdomain.example.com).

Here is what I did to prevent that:

server {
  listen 443;
  server_name evenotherdomain.example.com;
  rewrite ^(.*) http://example.com$1 permanent;
}