This reminds me a of a similar thing I did in Apache::AddrMunge, which is an Apache plugin module I wrote that mangles my mail address on my web pages.

The code looks like this:

         s{\b(mjd[-\w]*)
            \@
            (
             (?:\w+\.)?
             plover\.com
            \b)
           }
          {($a,$b) = ($1,$2);
            $a =~ m{-subscribe$} ? "$a\@$b" : "$a-id-$id\@$b"
          }gex;
[download]

It turns an address like mjd-perl-pause@www.plover.com into mjd-perl-pause-id-iws+bx9zvct@www.plover.com, unless the address is a mailing list subscribe address such as mjd-perl-memoize-subscribe@plover.com.

This page has a detailed description of a similar solution to a problem, but if you read it, be sure to start here instead and read backwards up the page. The end result:

  s{(.*?)(\`([^\']*)\')}
   {$pos += length $1;
    my $length = length $2;
    print ((' ' x ($pos)), "^", (' ' x ($length-2)), "^ ? ");
    my $r = lc <STDIN>; 
    $pos += $length;
    (substr($r,0,1) eq 'n') ? $& : "$1<tt>$3</tt>"
   }eg;
[download]