"Father forgive them."
Without making an eisegetical leap, where exactly does it say that?
"Father forgive them."
So, in other words it does not say that their sins were "not charged to them" any more than if you or I pray to the Father and say "Father forgive them."
The fact is that unless they come under the blood of Christ their sins will be chared to them on the last day. You wish to walk a theological tighrope that is not justified by the text.
"But I say to you that for every idle word men may speak, they will give account of it in the day of judgment." (Matt. 12:36)
When a man stands before the judgment seat on that great day, there are only two options. They can either stand their on their own account, or they can stand on basis of the finshed work of Christ. The unregenerate will not be able to point to one particular sin and say, "I have been pardoned from that one sin." No one will be so arrogant.
Thus your eisegesis of the text fails.