I don't think this is possible, but I want to check to be sure.
I would like to set a list to have

* Confidential= Local
* Service=      *       (this is the default)


Basically what I want is that the list only shows up on a LIST command
for people in the areas defined as LOCAL, but I want anyone anywhere
in the world to be able to subscribe.

Now you might ask "why would you want to do something silly like that".
The answer is actually pretty easy:  There are people who have an
email account in the LOCAL area (ie. a work account), but would rather
subscribe from a personal, off site ISP account (eg AOL, Compuserve,
etc).  When they find out about the list, I don't want them hassled
with being forced to use a particular account to subscribe from
(or the listowner having to manually add them).