Here’s a hybrid theory of the atonement that both upholds the intuitive idea that an innocent cannot be justly punished for another’s wrongdoing and enables one to hold to something like Penal Substitutionary Theory (PST). First, we need to see that justice may be satisfied in two possible ways.
Justice may be satisfied by punishment. If a guilty party commits a wrong, justice towards that guilty party can be satisfied when the party undergoes harsh censorious treatment, i.e., punishment. The problem with PST is that it permits an innocent to undergo punishment on behalf of the guilty, a judgment many have found repugnant. I can’t go down to the local execution board and offer myself in the place of a murderer, and thereby justly permit the murderer to be set free, can I?
But we also tend to think that justice can be satisfied by compensation. If a guilty party commits a wrong, he (or another on his behalf) can make-up for it by going above and beyond, providing extra merit to the wronged party. While we tend to judge that an innocent cannot be punished on behalf of another, we do not tend to see anything wrong with an innocent providing compensation on behalf of the guilty, e.g., paying a fine. A more difficult case–it doesn’t seem too odd to suggest that a murderer can be pardoned with the pardon having as a precondition someone else’s providing compensation on the murderer’s behalf; building hospitals, paying the wronged family, doing good-deeds, whathaveyou.
It’s this second view that enables us to say that the life, suffering and death of Jesus do not satisfy justice in a penal way. Instead, his life, suffering and death satisfy justice as a meritorious compensation for our wrongdoing. When Jesus was put to death, it was unjust. And on the basis of this injustice, he's owed something in return. This could be part of his meritorious treasure from which he compensates divine justice to satisfy it's demands on us.
So what makes this a hybrid theory? A subjunctive conditional move. We can say that the harsh treatment suffered by Jesus would-have been our punishment if we had instead received that treatment, though it isn’t literal punishment in the case of Jesus. This move enables us to see that we deserve the suffering that Jesus underwent and that his suffering exhibits the extreme demand of justice.
But the literal mechanism by which we are rendered justified in the eyes of the law remains compensation, not punishment.