The solution is so simple that it proves that any other being offered is simply stonewalling and avoidance. Jesus (everybody's favorite prime authority, except when He's inconvenient) said: "Render unto Caesar the things which are Caesar’s, and unto God the things that are God’s.” Ergo, prison sentences (Caesar's form of penance) must be served by those many who committed crimes of commission or abetting.
Except that the Pope himself was part of the abetting. I don't know if what Ratzinger did was a crime per se but morally he's as culpable as, for example, Cardinal Law. Which is of course why we will never see the Church take such action.