Is there an OS X Jabber client compatible with Cisco Jabber?

Is there any client or method to connect to Cisco Jabber in OS X? My company uses this and I hate to keep checking my RDP'd Windows screen just for Jabber when I'm working remotely.

I know there's the official Cisco Jabber client for OS X, but it requires a contract number to download. I know that itself makes it unlikely, but this historically had always worked under iChat (10.7), and under Messages.app (10.8). I'm currently using 10.10 and have tried all manner of settings under Messages.app and even Adium and can't get it to authenticate (matching server names and settings against the official Cisco Jabber client).

Has anyone been able to connect to Cisco Jabber via any third-party methods on a Mac?