User Tags per Row for PMs

[CoffeeLovesYou]

Hi,
Thanks to kh99, I currently have a certain number of user tags per row for Posts.
Here is the code I am using for Posts:
Hooked to postbit_display_start

PHP Code:

$rowlen = $this->registry->userinfo['field50']; 
if ($rowlen <= 0)
   $rowlen = 5; // default columns

$ranklist = explode('<br />', $this->post[rank]);
$this->post[rank] = '';
$col = 0;
foreach($ranklist as $r)
{
   if ($col >= $rowlen)
   {
      if ($this->post[rank] != '')
         $this->post[rank] .= '<br />';
      $col = 0;
   }
   $this->post[rank] .= $r;
   $col++;
}

$this->post[rank] .= "<!-- field50 ='" . $this->registry->userinfo['field50'] . "' -->\r\n";
unset($col, $rowlen, $ranklist); 


Now, how can I have the amount of user tags per row for PMs?
Can someone help me alter the code to work in private messages, please, and where to hook the plugin?
Thank you greatly