using "-nolisten tcp" with X

[Jim Breton <jamesb-debian@alongtheway.com>]

I have been aliasing startx to "startx -nolisten tcp" in my local users'
.bash_profiles in order to prevent X from listening on port 6000 on
startup.

However, display managers (at least gdm anyway) don't care about these
aliases, and furthermore I would like to make this option the
system-wide default, so I'm wondering in which file I might be able to
specify this option for the X server to use at every invocation?  It
needs to be in a config file so it won't get trashed if any X packages
are upgraded.

Also, under such a scheme, how would one then re-enable tcp listening
for an individual X session if that were desired for some reason?

Thanks.

(I am not on the list currently; please copy me on replies.)