不是很优雅，但应该可以。。。

$sep = " | ";
$args = array(
    \'before\'=>\'\',
    \'after\'=>$sep,
    \'category_after\'=>\'\',
    \'category_before\'=>\'\',
    \'title_li\'=>\'\',
    \'echo\'=>0     //return the string, don\'t echo
);
$str = wp_list_bookmarks($args);
//chop off the last separator...
$str = substr($str, 0, strlen($str) - strlen($sep));
echo $str;