You should be able to tell your browser about your OpenID account(s), so it can keep you logged in constantly. "Hey! Your OpenID login has expired. Please login again now, or hit 'Later' to see this prompt the next time you try to access an account."
Then, when you go to a website that supports OpenID, your browser can tell it, "Hey. Don't bother presenting us with a login prompt. Just check to see if you have any accounts associated with these OpenIDs."
Of course, it can't be that simplistic, because the site needs to verify authentication with your provider, not your potentially devious browser. But I feel like that is not a difficult problem to solve.
It's one-and-a-half steps. The first "half" step is "Logging in," because you only have to do it once per browser session. The first real step is: "Go to the site." Done.