Move the source of payment to human flesh.
The payment comes from man, not from God.
The problem it faces
The fact that an intra-trinitarian payment is nonsensical means that the payment must come from somewhere else.
The move it makes
The answer is found in Chalcedonian tradition of God's impassibility. Because God is immutable and cannot be harmed by his creatures, then the repayment must be drawn from man's account and not God's.
The new problem it opens
Humanity lacks the inherent value necessary to satisfy the demand.