For the sake of discussion:

Where in the regulation is it foreseen that the airlines needs to explain to the passenger what the passenger needs to do to fulfill the conditions of contract? The passenger insisted to board the aircraft with (still assumingly but likely) too heavy hand luggage and refused to check it in.

What you propose is not only an uphill battle but to my belief not within the language of the regulation and could only have success if the ECJ issues another ultra consumer friendly decision.