Yeah, we had the same issue as our login credentials are associated through LDAP, so users can't just change their Jive password. We removed that functionality altogether from the login page. I can't remember if it was a system property or a template/theme tweak, but if you'd like I can go back through my records and find out exactly.
I think what we did was turn the functionality off by a system properties change, and then added verbiage similar to what you suggested through a template change. It was relatively painless, whichever it was.
Here's the location of the setting in 4.5. We disabled this too, for the same reason.