My things have come a long way since this thread. :-)
Id say hacking this into the regex engine is probably a good thing. And i suspect that its probably easier to do so than to hack PCRE into perl. Even perls own regex engine is not easily properly pluggable due to a lack of hooks into sv.c's re_dup(). I suspect that getting the PCRE engine would have the same problems. Which actually reminds me, we need to make sure that Perl 5.10 has the appropriate hooks so that making pluggable regex engines for perl 5.10 and later is easier.