This is untested and it’s a long time since I hacked the EasyNewsletter code.
Backup your backend.php file first

In backend.php find each instance of :
while($i < $num){
$mail = new PHPMailer();
Then replace with :
while($i < $num){
$newsletter_newsletter = str_replace('[+fullname+]', mysql_result($result,$i,"fullname"), $newsletter_newsletter;);
$mail = new PHPMailer();
In your newsletter template add the placeholder
[+fullname+].
Test it and find it probably doesn’t work