Wireless is going to be tough. If you can get away with wired, some of the sim racing sites sell adapters that turn the pedals from wheel sets into stand alone usb devices. The pedals are just 10k pots though... no additional circuitry... so you could build a set from scratch or better yet buy a "crappy" set on ebay from someone that upgraded their pedals.
*EDIT*
If you don't mind hacking, wireless gamepads typically use pots in the 10k range as well, so you could make/hookup a wireless set anyway.
I'll say this though. While mame doesn't care if your wheel and pedals are different usb devices, nor do most racing sims, older pc arcade racing games might. I know outrun 2006 (without my hacks) throws a fit if you have more than one usb controller hooked up.