I suggest you leave the system perl alone. Messing around with the system perl (and vendor supplied modules) can result in an unstable OS. It's trivial to install your own perl elsewhere on the system. See this thread for details of the problem, various solutions and other OSX prerequsites which may be requied.

Update:

"...force it to reconfigure"

for future reference if you want to reinitialise the configuration of cpan:

cpan> o conf init
[download]