What about this? Wall is 0.25 meter width (1/4 of current width and also 1/4 of grid). It will only be eyecandy. Game will see it as 1 meter thich wall (pax won’t walk on it, nothing can be placed on it except doors and windows, the rooms cannot be added on it, areas will be covered under the wall) but players will see it as 0.25 meter thick wall.
Of course current doors and windows will need to be changed to adjust these walls.