Then I would get wingnuts to fasten the seat down. The screw and wingnut would need equal or greater tensile(?) strength in comparison to the OEM screws they are replacing (obviously for crash safety). The fly in the ointment from my POV is that the way the seating bolts are arranged, it may not be possible to mount the seat onto screws that are "sticking out" of the floorboards.
My other idea was that maybe I could mount the OEM passenger seat onto an aftermarket seat rack that I mount to the floor on the hunch that the aftermarket seat would me more "flexible" to what I had in mind.