Have you tried creating an autobundle? That will create a snapshot file that contains the names of all of the installed modules along with their version numbers. You just have to look at the modules with a version number that is either 0 or undef.

You can use my cpan(1) utility (which comes with CPAN.pm):

$ cpan -a
[download]

Or, if you want to drop into the CPAN.pm shell, you can issue the 'autobundle' command.

$ cpan
cpan shell -- CPAN exploration and modules installation (v1.7601)
ReadLine support available (try 'install Bundle::CPAN')

cpan> autobundle
[download]