I strongly recommend that you treat it more-or-less like a “install CPAN as a non-root user” situation, as is very well-documented elsewhere. Set up your own directory, entirely separate from the system ones, and designate this as your installation target for CPAN. Put it ahead of the others in PERL5LIB. When cpan is properly configured, it works normally.
OS/X uses Perl for a lot of things. You don’t want to put that in jeopardy, so keep your hands off sudo. It also frequently upgrades the Perl version when going from one major OS-release to the next.