It looks like there were two options in the promo page: "Register" and "Login", you should try with login.

Well, not anymore, since now it takes you to the promo form if you are already logged in.

Thanks! I feel so stupid not even trying the link and seeing it had a /promo in it. It worked just fine!

It seems you can't get the additional bonuses from linking Facebook, etc. if you had the promo.