I have the Gamestop DDE, the joined Trill is linked to your registration code, and should be showing up if you start a new character. If not, let Cryptic know about it, all the bonuses are tied up with the reg. code in their databases.
I'm 100% positive that if you currently have a Trill Character you must make a new one to get Joined Trill. As Washu said you have to create a dummy character to get to the C-Store, grab your pending items then create a new character.