Am I missing something?

  print 
   q|^.*(??{                                    })\z| =~
   m|^.*(??{$&ne'^.*(??{'.substr($&,7,36).'})\z'})\z|

  # outputs 1
[download]

Update to japhy's update: In that case, why not simply:

  $re = q{^.*(??{$&ne$re&&'(?!)'})\z};
[download]

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print