This could be useful for other applications as well, but I would still push to get split-brain DNS configured if at all possible before falling back to this option as a last resort. While it’s attractive consider the overhead of maintaining and documenting additional DNS zones. Probably not an issue for the admin doing this, but for someone else taking a look at your environment you’ll probably raise some “WTF?” eyebrows.

Doug Lawty expands on Geoff’s idea a bit and uses Dnscmd.exe to work around a GUI limitation to create the exact zone you need: http://blogs.technet.com/dougl/archive/2009/06/12/communicator-automatic-configuration-and-split-brain-dns.aspx