# MyConfig.pm

# Stuff common to all configurations
$CPAN::Config = {
   'applypatch' => q[],
   # bunch of junk snipped out
};

if ($Config{osname} eq 'foo') {
   $CPAN::Config->{build_dir} = '/work/builds/foo';
}
elsif ($Config{osname} eq 'bar') {
   $CPAN::Config->{build_dir} = '/work/builds/foo';
}

1;