I'm not sure if this will buy you any improvements, but you might try the qr operator. You might even already be using qr depending on what &composeRegex returns.

Quoting from the documentation:

qr/STRING/msixpodualn

This operator quotes (and possibly compiles) its STRING as a regular expression. STRING is interpolated the same way as PATTERN in m/PATTERN/.

I think this example (also from the documentation) gives a good idea of what is possible.

my $sentence_rx = qr{
   (?: (?<= ^ ) | (?<= \s ) )  # after start-of-string or
                               # whitespace
   \p{Lu}                      # capital letter
   .*?                         # a bunch of anything
   (?<= \S )                   # that ends in non-
                               # whitespace
   (?<! \b [DMS]r  )           # but isn't a common abbr.
   (?<! \b Mrs )
   (?<! \b Sra )
   (?<! \b St  )
   [.?!]                       # followed by a sentence
                               # ender
   (?= $ | \s )                # in front of end-of-string
                               # or whitespace
}sx;
local $/ = "";
while (my $paragraph = <>) {
   say "NEW PARAGRAPH";
   my $count = 0;
   while ($paragraph =~ /($sentence_rx)/g) {
       printf "\tgot sentence %d: <%s>\n", ++$count, $1;
   }
}
[download]

I hope this helps, even if only a little.

Cheers,

Brent