Here is how to make a perl image for anaconda (the installer for fedora, redhat, centos etc), which will allow you to use perl in the %pre stage. I've used staticperl from http://software.schmorp.de/pkg/App-Staticperl.html. There is a small and a big staticperl version, which includes just a few or quite a lot of perl modules respectively.

# make an ext2 image of 50 megs and format it ext2, and mount
dd if=/dev/zero of=perl5.img bs=512 count=100000
losetup /dev/loop0 ./perl5.img
mkfs -t ext2 /dev/loop0
mount -t ext2 /dev/loop0 /mnt

# copy the files and unmount
cd /mnt
wget http://staticperl.schmorp.de/bigperl.bin
cd ~
umount /dev/loop0
losetup -d /dev/loop0

# thats it!

Now just put that somewhere accessible via http and specify it as an update image when you boot to anaconda.
linux updates=http://some.website.com/path/to/perl5.img
Then use it in %pre with...
%pre --interpreter /tmp/updates/bigperl.bin