Google will love you.

function spin($pass){
    $mytext = $pass;
    while(inStr("}",$mytext)){
        $rbracket = strpos($mytext,"}",0);
        $tString = substr($mytext,0,$rbracket);
        $tStringToken = explode("{",$tString);
        $tStringCount = count($tStringToken) - 1;
        $tString = $tStringToken[$tStringCount];
        $tStringToken = explode("|",$tString);
        $tStringCount = count($tStringToken) - 1;
        $i = rand(0,$tStringCount);
        $replace = $tStringToken[$i];
        $tString = "{".$tString."}";
        $mytext = str_replaceFirst($tString,$replace,$mytext);
    }
    return $mytext;
}

$s = spin("{spin|spun} {stuff|shit}");

echo $s;