Second product could be called "Feed", to play off the Cell Force XT name, by calling the tandem....the Force Feed Stack. The theme being that you're force feeding the creatine to your muscles and maximizing the capacity of the first product by adding the second.
A print ad could show a guy that's totally spent after his last hard set, covered in sweat...
Caption might say something like "Your muscles are are now shocked and starving...you need the overwhelming recovery only available when you FORCE FEED them!"
Then youd list the stack and individual products' names. Any trainee can relate to the concept of needing to forcefeed muscles after a grueling workout, so this concept would be familiar to and hit home w/ anyone looking to get a leg up on fast and full recovery. I think it's an name/idea that works.