SSL for multi domains on single GWIA

I have 6 domain names that my single GWIA can send and receive for. We host mail for 6 different divisions of our organization, which many years ago went out and got their own domain names. :/ Right now, I have a single domain SSL certificate installed in my GWIA for our most heavily used domain so we can get as many transactions as possible secured with SSL.

I've been reading about multi domain certificates and UC (Unified communications certificates). Has anyone done this and installed on GWIA?