If you're ok with the system build you can install modules locally without building a whole new Perl. I have previously posted instructions.

But why is /usr/local/share/perl/5.10.0/Module/Build/Base.pm executing?

My guess is that you're executing the system's cpan or that it's executing your system's Perl. Make sure you're executing your own cpan, and make sure you its shebang line points to your own Perl. You shouldn't have to change any of cpan's configuration if the right tool is being used.