I don't think you realize what it takes to make the Perl regex engine work. You can't just rip it out of Perl. To make it work you'd probably end up just embedding perl into an executable, which would require even more footprint.
Besides, every good system should have Perl so the footprint you should be comparing is grep.pl vs. grep.exe (to borrow a file naming convention from a different platform). I think the pendulum will swing the other way. :)
Update: The two grep's weigh in a 16K and 820 bytes (smaller than grep.exe or much, much smaller).
(but my friends call me "Tye")