If you are comfortable with the script you have used you can try updating the Universal Email code to make use of the same script code that you tested with. This would be in the WA_Universal_Email > mail_PHP.php file. In here you can find the mail call that is around line 257. This is the point in the script where the mail call is made using all of the global values for the Solution Recipe. You can alter the code at this point to use your code instead.
This would be a custom implementation though and not something that we could offer support for.