[tnguy3n]

To make adding referrer as an option at registration page.
Open register template,
FIND:

<input type="text" class="bginput" name="referrername" value="$referrername" size="50" maxlength="250" />

BELOW, ADD:

<br><input type="checkbox" name="addreferrer" value=""> Add $referrername to your buddylist?

Then from amykhar's hack,
REPLACE:

if($referrer)
		{
					// Put it in the database.
				   	$DB_site->query("
				   	UPDATE " . TABLE_PREFIX . "usertextfield
				   	SET buddylist = '" . addslashes($testreferrerid[userid]) . "'
				   	WHERE userid = $userid
						");
		}

WITH:

if ($referrer AND $_POST['addreferrer'])
		{
					// Put it in the database.
				   	$DB_site->query("
				   	UPDATE " . TABLE_PREFIX . "usertextfield
				   	SET buddylist = '" . addslashes($testreferrerid[userid]) . "'
				   	WHERE userid = $userid
						");
		}

Did not tested