That's why you nominate Estrada.
I doubt this would have much impact on the cases he deals with as a Justice. It seems to apply only to the particular cases in which he was previously involved.
And he's only been AG for less than a year. My suspicion is that the rule would only preclude the attorneys actually arguing the cases, not the AG.
Interesting viewpoint, but I doubt much recusal would ensue; the Supreme Court isn't in the habit of abiding by federal/congressional wishes. Especially when the real precedence for this situation would be Taft, who became a Supreme Court justice after serving as president.