It's not in Windows registry. You can either pass command line switches at install time or use an MST to set these manually.
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/jabber/10_6/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and-installation-guide/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and_chapter_01011.html
IMO, you would be better off fixing whatever DNS problem you have so you can use Service Discovery instead.