Wordpress Social Invitations share custom url for logged user

functions.php

add_filter( 'wsi/placeholders/custom_url', 'wsi_my_custom_link' );
 
function wsi_my_custom_link() { 
  global $current_user;
  get_currentuserinfo();
  
  //return home url with ref username
  return site_url('?mref='.$current_user->user_login);
  
  //return the same shortened with goo.gl
  //return Wsi_Queue::shortenUrl(site_url('?mref='.$current_user->user_login)); 
  
  // you can also return ID $current_user->ID
}