What I suggested works. You can gift SL to someone who has RIFT through Steam, have them give you the key and you can activate it via Trion's website I know the sale is almost done, but there you go.
That's good to know there's a way to make it work. The other things I read suggested you could view your code if you logged onto steam on a different computer or reinstalling your own steam. Very strange that it would be this way, and not very reassuring, but glad it can be managed somehow.