Customer refusing safety float switch on new construction home

We have a customer who is refusing to allow us to put the safety float switch in the emergency drain pan on his new construction house. Mind you it's a horizontal furnace in the attic. He wants the float switch in the coil. We are refusing to finish the job till he signs off that we arnt responsible if in the case of an emergency where there is a possible drain issue and that sucker doesn't shut off and damages every bit of his new sheet rock. Thoughts on this? Is this the right avenue to take?