What I've discovered recently is that if you want to be completely independent or if you need to use a newer version of Perl than is what installed system-wide then it is also quite easy to install your own Perl interpreter in a private directory (just remember to follow INSTALL and add -Dprefix='/some/dir' to Configure's args). Then you just add this new perl into your PATH - and you can use perl -MCPAN -e shell or cpanp as usual without fiddling with parameters to the *.PL scripts.