Alder I think you are confusing the requirement for a step up from coach to the hard requirement for a 1st class seat. But if I am wrong you can still make them pay for the 1st class seat. But a higher class of service is defined as block over 10, etc., block over 16 demands:
iv. iii. If the deadhead is scheduled for more than 16 hours duty, the following shall apply:
(a) The flight must be a non-stop flight; and
(b) A special booking priority shall apply to deadheads scheduled over 16 hours. That priority shall be:
(1) Discounted first class;
(2) Full fare first class;
(3) Business class; and.