[CentOS] Prevent network setup from changing the hostname

How can I block network setup (via NetworkManager) from changing
the machine's hostname whenever the network configuration changes?

The problem: When my graphical login session starts, the xauth
database gets an token that is labeled with the hostname at that
time. If there is not yet a network connection, that will be
"localhost.localdomain". When a network connection is then made
(my wireless connection needs the key from my login), the hostname
changes. That breaks X session sharing because there is no xauth
token that matches the current hostname. If I get a root shell
with "su -", commands launched from that shell cannot access the
display. If I set up an ssh connection with "ssh -X", I get a
complaint about missing xauth data.

On systems with an "ONBOOT=yes" network connection, there is no
problem since the hostname is set before the X session starts.
It's just when the hostname changes during the X session that
there is a problem.

I am running CentOS 6, fully updated. It's taken me a long time
to track down the root cause of this problem. Now I just need a
solution, preferably something less ham-fisted than "xhost -".

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.