All you need is to log onto your ESO account, regardless if you launch through Steam, etc, goto add game key, put the key in that you get with the digital collector, then restart the game and your good to go. They may ask for payment again if your an eso plus member, just go through the steps, but it won't actually charge you unless your due date is today, etc.
Is that, in any way, possible? I bought Morrowind upon release and would consider upgrading my version now in order to get some of the digital goodies that the Digital Collector's Edition provides.