So as I understand it the question is how to rationalize the configuration of your app. Where would you like your config file to be? I think you need to first of all figure that out.
Then you need to figure out how to inform your app of that location. You may want to think about what your ideal format would be. There are probably several modules in CPAN to read those config files. One of your lines would be the location
of your
SQL::Library file. So you code might end up as
my $config = [....code to read config file];
.....
my $sql_lib=new SQL::Library {lib=>$config->sqllib_path()};
