//
// index
//
<fb:editor>
<fb:friend-selector uid="<?php echo $_POST['fb_sig_user']; ?>" name="i0" idname="i0" />
<div id="d0">
<div style="display:none" id="loadmsg">Loading...</div>
<input id="loadbutton" clicktohide="loadbutton" type="button" clickrewriteurl="http://URL/afs.php?d=0&uid=<?php echo $_POST['fb_sig_user']; ?>" clickrewriteid="d0" clicktoshow="loadmsg" value="Add Another" />
</div>
<input type="submit">
</fb:editor>



//
// afs.php
//

<?php
$d = 1;
if(isset($_GET['d'])){
        $d = $_GET['d'] + 1;
}
?>
<fb:friend-selector uid="<?php echo $_GET['uid']; ?>" name="i<?php echo $d; ?>" idname="i<?php echo $d; ?>" />
<div id="d<?php echo $d; ?>">
<div style="display:none" id="loadmsg">Loading...</div>
<input id="loadbutton" clicktohide="loadbutton"  type="button" clickrewriteurl="http://URL/afs.php?d=<?php echo $d; ?>" clickrewriteid="d<?php echo $d; ?>" clicktoshow="loadmsg" value="Add Another" />
</div>