This isn't something you can fix the way you want it to be fixed. Pedals are weird and they don't have any standardization. Even worse, most programs, yes including mame aren't designed to work with pedals, because, again, pedals are weird. A negative number at rest, 0 when half pressed and a positive number when fully pressed is perfectly normal for a lot of pedals. I also got a laugh out of the "it'll mess it up for every other joystick game" comment. You do know that you will have to do a custom config for virtually every single mame game right? The misc buttons, shifters and pedals aren't standardized in mame and thus you will have to remap every single racer individually. Sure you can probably get away with a unified mapping for the pedals, but since you'll absolutely have to remap the buttons for every game there isn't much point to it.