I don't know if it will help, but I just saw this on comp.lang.perl.misc,concerning a similar problem.

#by Janek Schleicher
#favor using a module: 
use Regexp::Subst::Parallel;
my $replaces_str = subst($string,
   qr/A/ => 'Y',
   qr/B/ => 'Z'
);
######################################
#Discussion:
#using a hash
my %substitute = (A => 'Y',
                  B => 'Z');
my $keys = join "|", keys %substitute;
s/($keys)/$substitute{$1}/g;
#Disadvantages are that it becomes slow, 
#when there a lot of different expressions, 
#and it can lead to problems if there are some regexp characters insid
+e. 
###############################################
#It's often extremely useful, 
#if you know that the matches can be matched with a more general one, 
#e.g. they are words: 

s/(\w+)/$substitute{$1} || ""/ge;
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