Get the list of your installed 5.8 modules:

#+BEGIN_SRC sh
    % perl -MExtUtils::Installed -e'print join("\n", new ExtUtils::Installed->modules)' > module.list
#+END_SRC

then install Perl 5.10:

#+BEGIN_SRC sh
    % wget http://www.cpan.org/src/perl-5.10.0.tar.gz
    % tar xzf perl-5.10.0.tar.gz
    % cd perl-5.10.0
    % sh Configure -de -Dprefix=/opt/perl -Duserelocatableinc
    % make && make test
    % sudo make install
    % /opt/perl/bin/perl -e 'use feature qw(say); say "hi"'
#+END_SRC

and then re-install your modules with cpan `cat module.list`.