I got the Civ V: GOTY edition and got the key. Hoping that will activate on Steam. Can't try it at work as they have Steam blocked off. =/
I used to use LogMeIn [logmein.com]
to activate games on Steam. Now, I find it easier and faster to use Chrome Remote Desktop [google.com]
Now that you can start downloads from the Steam website, I'd be surprised if the site didn't soon let you activate games there, as well.