Not sure if you're handy or know someone how is ?
I made a bracket recently that could be fitted quite easily with the pedal box in the car and there was no holes to drill. It's also adjustable so it's easy to position it for the switch you end up using.
It was made from one piece on metal, about 10 mm square which I milled a slot in, but could also have a slot made with a hacksaw, then filed with a wading file to make it wide enough. It needs to ba able to fit over the edge of the steel used in the pedal box, about 2.5 - 3 mm wide. In to the side of that, I drilled and tapped it for an M4 grub screw so that this piece of metal could be clamped on to the edge of the pedal box, then use the grub screw to clamp it on with. On to the side of this clamp, I welded an M12 flat washer as approx 90 degrees to the side opposite that of the grub screw. The Switch then mounts in the washer, then it's a simple matter of put it on the edge of the pedal box next to the brake pedal, sliding in to a position where the button on the switch is pressed in about 1/2 way and locking in in place with the grub screw.