I have bought ESO on release and have two copies of ESO retail including the 10.000 unit limited edition Heroes Guide pack and the imperial edition. It was a while ago I played and I want to get back into it, but I really want to play on Steam though now as it is supported, but how can I get an unlock code from my retail games to unlock it on Steam?

I really really hope it is not expected that I buy yet another copy of the game as that would be an extremely greedy practice. I am a small indie game developer myself on Steam and I know how easy it is to generate keys and it is obvious to give old fans who actually bought my game elsewhere before a Steam key.