In order to get a coupon for a free Neuro Sonic drink, all you need to do is create a new drink. That may sound daunting, but it should only take a few minutes (though you might want to make sure they sell these in your area first.)
Hopefully these taste better than the concoctions I made as a kid in buffet restaurants. I never could quite get the perfect mustard to ketchup ratio in my coke. And don't even get me started on how much pepper was needed to balance out the cumin!