In this case i think the best thing for just one setting would be
an environment variable.
+1
+1
Yes, you might like it, but it doesn't work. There is no easy and
portable way to set environment variables for all shells which work for
users and root and which persists through su and sudo. Plus then you're
abusing the file where you are configuring the environment variables as
a generic configuration file, exactly like you want to avoid.