That's rarer than on the Wizards.com boards. I think the archived forum is there mainly for safekeeping in the event of a new server shuffle.
But you can sneak your attachment in a thread that will get archived; or you can just keep it on your hard drive and re-attach it in a new thread if it one day disappear; then you'll just have to update your profile.
By the way, Ferret, you should use that opportunity to prune your sig. One quote is long enough, two or more are too much.