Everything cpan does can be done manually without too much effort. It doesn't install modules at all; it simply downloads them and lets their Makefile.PL or Build.PL do the installing.

tar xvzf foo.tar.gz
cd foo
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then either

perl Build.PL --install_base "$HOME"
./Build
./Build test
./Build install
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or

perl Makefile.PL INSTALLBASE="$HOME"
make
make test
make install
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Tell Perl how to locate the modules you install by stuffing the following in your login script:

export PERL5LIB="$HOME/lib/perl5"
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There are two catches:

• You'll have to satisfy dependencies. IIRC, Makefile.PL and Build.PL will tell you which dependencies aren't satisfied.
• Dependencies on external (non-Perl) libraries will be hard to install. Normally, one would use the OS distribution's package system, but that's not available to you. If you want to install XML::LibXML (for example), you'll have figure out how to install libxml2 (the underlying C++ library) into your account if it's not already installed on the system.