You could use require instead, as it happens at runtime instead of compile time. The downside is that you need to know where the file is of course.

if (<check that the file exists>) { 
    require 'settings.pm'; 
    settings->import();
} 
else { 
    $::CONFIGPATH = "C:\\configdir\\config.pm"; 
}
[download]

Or you could use it in an eval, and run the else if it fails.

eval "use settings";
if ($@) {
    $::CONFIGPATH = "C:\\configdir\\config.pm"; 
}
[download]