I liked merlyn's suggestion of teaching from the Llama book. But I had a thought on how you might condense.

You mentioned that your target audience already have experience with C++. Take the philosophy of leading a horse (or budding Camels) to water, rather than trying to force him to drink. Rather than attempting to teach Perl in a day, teach those parts of Perl that are easy to see as advantageous strengths over, say, C++. If they're thirsty, they'll start with that kind of an introduction and run with it.

For example, while teaching out of Llama, specifically go over topics such as hashes, lists/arrays, regexps, go heavy on DWIM'ery, file operations, including specifying alternate input record separators, show a trick or two with split, a trick or two with map. Dynamically create code and eval it. Delve a little into references and data-structures. Use that to lead into doing a Schwartzian Transform with short-circuit fallthrough to demonstrate how to sort on multiple criteria... those are just a few thoughts.

I guess what I'm saying is that you probably can't teach Perl in a day, but you can teach why this group should invest the personal time required to learn it. Stress quick development time, rich syntax, extreme flexibility, etc. Even stress extensibility; the fact that Perl can incorporate C/C++ in its code, and the fact that C/C++ code can embed Perl. And by all means, show off CPAN. You have a good opportunity, in that you're talking to already reasonably coherent programmers. You will be most successful in turning a few of them into Perl programmers if you devote your time to showing what is in store for those who grab the torch and run with it.