The best way AFAICT is to use the environment variable PERL5LIB. So setting the environment variable PERL5LIB to, say, /foo/bar:/bar/foo before invoking perl will add /foo/bar and /bar/foo to @INC. If you want this to occur more than in your shell, you'll need to specify what sort of OS you're running.

Another, less good way is to do an alias perl='perl -I/foo/bar -I/bar/foo' (or its equivalent, if you're not running bash); IMHO this is less correct however.

HTH...