Three possibilities:

1. If you want the contents in a file, use getstore instead of get and writing it out yourself:

   perl -MLWP::Simple -e'getstore("file:/cpan/authors/id/P/PM/PMQS/Compre
   +ss-Raw-Zlib-2.060.tar.gz", "Compress-Raw-Zlib-2.060.tar.gz" )'
   [download]

2. Patch your copy of LWP::Simple with a new method (say: getRaw() ) that returns the content rather than the decoded content::

   sub getRaw ($)
   {
       my $response = $ua->get(shift);
   ##    return $response->decoded_content if $response->is_success;
       return $response->content if $response->is_success;
       return undef;
   }
   [download]

3. use lwp-download [-a] <url> [<local path>]:

   lwp-download file:/cpan/authors/id/P/PM/PMQS/Compress-Raw-Zlib-2.060.t
   +ar.gz
   [download]