Theoretically, you should be able to install Perl modules from CPAN like this:
:HELLO MGR.PERL
:/bin/sh -L
$ perl -MCPAN -e shell
cpan>install MPE::CIvar
But you may have a few problems configuring CPAN. First, make sure the /dev directory is readable to MGR.PERL, otherwise the ReadLine module will not work at all.

(Even with /dev set correctly, it still will not work quite right, but you can still use the CPAN shell.)

Second, if you are behind a firewall, as most HP3000s are, you may need special ftp settings.

I use:

export FTP_PASSIVE=1
In fact, I put it in /PERL/PUB/.profile so it gets executed automatically when I do /bin/sh -L. My .profile has:
umask 022
export FTP_PASSIVE=1
The umask is so that the permissions will be set to that other users can use the installed modules.