you can add a return path in the WA_Universal_Email/WAUE_contact_1.php by editing the third argument of the WAUE_Definition
$WA_MailObject = WAUE_Definition("".($WAGLOBAL_Email_Server) ."","25","return_address@domain.com","","","");
The envelope from setting is added to the email using the -f parameter of the mail function:
you will need to edit that in the mail_PHP.php file:
$mailObj = mail($mailTo,$mailSubject,$mailContent,$mailHeader, '-f return_address@domain.com');