What you're trying to establish is that you didn't have possession and control over the vehicle to "fix" the issue. Without the registration papers showing the actual owner and corroborating documents or evidence showing when (and for how long) the vehicle was under your control, the judge will likely find you guilty (unless he or she is in a pleasant mood).
This is NOT legal advice. No attorney-client relationship exists.
I am quite sure that driving without registration is not an owner's responsibility ticket. You are liable for it as the driver of the car. You will need to provide proof of registration and insurance in order to reduce the fines.