Side note...

I've faced this problem. I tackled it. (With actually some good help from my first line manager - possibly higher, I'm not sure.) We now have multiple versions of perl in production. Older code uses older perl, new code uses newer perl. In fact, my code runs on perl 5.8.7 on Unix/Linux and 5.8.6 on Windows (due to a problem we had on unix/linux which wasn't relevant to windows - no desire to upgrade windows again), while the code from other teams runs on 5.8.1 or 5.6 or even 5.005.

The 5.8.7 install has the 5.8.6 lib directories in its hardcoded @INC. The lib directories are shared across all platforms (including Windows, I think). And I have a way of hacking in new CPAN modules at runtime (thus far, they're all pure perl which makes it trivial, not sure if I'm brave enough to try XS or Inline::* code...).

This is a fairly large software company. (Our building has about 2500 people - software developers and support, such as IT, management, customer service, HR for software development, but not sales, corporate management, lawyers, etc. And we're not the only developers in the company.) It's just a matter of aligning the priorities and making sure everyone gets what they want. Management wants to ensure nothing is broken. Thus, keep the old versions of perl. Management also wants fast development. Thus, new versions of perl need to coexist in a way that allows us to get new CPAN modules.

I actually got this ball rolling when we started investigating XML-based technologies. There was no way I was going to do that by hand - I got my manager behind the idea that we needed XML::Twig. And we pushed from there - "No way to hit our dates without this." As in, yes, we can do it, but not by the end date you want it to be done by. That brought extreme amounts of pressure to resolve the situation.

Of course, if your management says, "Ok, we'll move out the dates," then that's what you do. You rewrite stuff that would work fine if they were willing to have a parallel perl that was up to date. But they're willing, instead, to pay you to reinvent some wheels. That is their perogative. ;-)