Is there a way to exclude user-specified files or directories from participating in merges?

[Brent Goodrick <bgoodr@gmail.com>]

Suppose I create a git repo called central.git on a machine I will
call "central". In that central.git repo, I put these files:

  work.sh
  home.sh
  generic.sh

When I clone the central.git repo on to a different machine I will
call "work", I want this fileset to be pulled:

  work.sh
  generic.sh

But not the home.sh file.

Similarly, when I clone the central.git repo on a machine I will call
"home", I want this fileset to be pulled:

  home.sh
  generic.sh

But not the work.sh file.

What I think I need are two branches, one called "home_branch" and
"work_branch", but read on for the twist:

Say I'm working on editing the work machines fileset on the work repo
I had cloned originally from central.git, and commit a change to both
generic.sh and work.sh.  I do a git-push to an appropriate remote
branch I have set up on the central.git repo, so that I can do a
git-merge type of integration on the central machine in the
central.git repo into the other branches (i.e., into the home_branch),
specifically so that the home_branch gets updated with the change to
the generic.sh file.  However, I want the home_branch to be updated
with the change I made to generic.sh, but I don't ever want the
work.sh to show up in the home_branch that would occur during a normal
merge. Likewise, I would not ever want the home.sh file to participate
in merges from the work fileset back over to the home fileset (and
likewise I would not ever want to see the work.sh file show up on the
home_branch).

The above should apply for all files certain special directories. For
instance, if I were to have a work_files directory and a home_files
directory, then the the work_files is for the "work" machine (and
work_branch) and the "home_files" is for the "home" machine (and
home_branch).

How do I mark certain files and/or directories (via relative file
paths or with file globbing) on certain branches to be excluded from
being merged into all other (or a specified list of) branches?
Ideally I would want to only have to add some logic to the .git/config
file in the central.git repo that specifies the exclusions/exceptions,
and not have to remember to make corresponding changes into any of the
other repos that are cloned from it. Is this possible?

Also, is there a way to avoid the home.sh file from ever being added
to any file underneath the .git directory of the repo I cloned on the
"work" machine. I would not want there to be any risk that anyone with
network access to the "work" machine (say, a sysadmin with sufficient
privileges) to be able to see any form of the home.sh file since it
exists on some branch in the .git directory.

Thanks,
Brent