Why is Perl knowledge a requirement? I've been writing Perl in my new job since June and almost the entire team of 10 (myself included) knew no Perl before joining.
Check that your candidates know how to develop software, make sure they are comfortable with functional programming so they don't break anything, and give them a couple books (programming perl & higher order perl) to read for a week after joining.
Same here. At my current job I knew exactly 0 perl to start with. I haven't learned all the object oriented stuff yet, but I'm cruising (and have been for at least the past three months or more) at 4 mo. in, and I was capable of writing some of the simple stuff after a week or two.