The hack didn't end up working. I wasn't able to replicate it the following Monday which was very disappointing so we came up with a new workaround. We purchased a domain name that is vague enough that it could apply to all three of our business lines. That is what we use for the branding domain now, so that we can make use of the link tracking functionality for all emails regardless of sender.
Now when a reader hovers over or clicks on a link in an email they'll see the generic domain name but when they click on it, it disappears after a second and the full intended url appears.