From the command line, simply do:
$ cpan
cpan[1]> install <package-name>
Or directly:
$ cpan <package-name>
If you don't know the precise package name, try:
$ cpan /<package-name>/
# e.g.:
$ cpan /frenchrevolutionary/
If the package to install is like Module::Package, use double quotes like this:
$ cpan
cpan[1]> install "Module::Package"
Ebuild
See the note in Gentoo's Submitting ebuild: