Adding a Commercial Domain Cert

[buee]

I have what I'm sure is a very simple question, but it's been bugging me. I'm trying to generate a CSR for a domain that's configured on my Zimbra server. The domain that I'm trying to get a CSR for is NOT the default domain on the server.

I was following Administration Console and CLI Certificate Tools - Zimbra :: Wiki

But it specifically says

Generating Multiple CSRs using the Administration Console

Currently the Administration Console only supports having one Certificate Signing Request (CSR) and private key at a time. Generating a new CSR overrides the existing one and generates a new private key. To generate more than one CSR, move both the CSR and key from the directory it is generated in (E.g. /opt/zimbra/ssl/zimbra/commercial directory/) before generating another CSR.

I've already got one commercial certificate on my main domain, but I need another domain to have a cert so the end users don't get the goofy errors from Outlook. I tried redoing the main certificate with a CSR including my second domain as a secondary name, but the Network Solutions CSR program kicks it out and says that it's the wrong domain name. Anyone done this and can provide a rudimentary process to do it?