I think you shouldn't underestimate the length of $needle in the search of THE FIRST POSITION of it's last occurrence in the string. I improved the posted function, with added support for offset. I think this is an exact copy of the real function:

<?php
if(!function_exists("strripos")){
    function strripos($haystack, $needle, $offset=0) {
        if($offset<0){
            $temp_cut = strrev(  substr( $haystack, 0, abs($offset) )  );
        }
        else{
            $temp_cut = strrev(  substr( $haystack, $offset )  );
        }
        $pos = strlen($haystack) - (strpos($temp_cut, strrev($needle)) + $offset + strlen($needle));
        if ($pos == strlen($haystack)) { $pos = 0; }
        return $pos;
    }/* endfunction strripos*/
}/* endfunction exists strripos*/
?>