Filtering specials

gistfile1.txt

<?php
  // in functions.php?
  Hooks::addFilter('specials_filter', 'filterTheSpecials');

  function filterTheSpecials($filter)
  {
    //  limit to physical products only
    $filter->limitTo('PhysicalProduct');
    //  or limit to the Computer category
    $filter->limitTo('Category', 'Computer');

    return $filter;
  }