The g25/g27 pedals will work but you will have to rewire some things I think...there's a video on youtube:
http://www.youtube.com/watch?v=eAhNhWNNm-8 This will show you how to do it, though you won't be able to use the clutch. If you do this you could buuy a NIXIM mod or AP electrix load cell mod to make them even more realistic.
A second alternative is you could buy the ECCI pedals that are made for the DFGT to be used on PS3. You get a gas and brake and great build quality, but they're pretty expensive I think, take a look here:
http://ecci6000.com/6000_momo_01.htm
Quote from them:"ECCI offers TRACKSTAR 6000 pedal units that are plug compatible with Logitech force feedback wheels. Loaded with all the innovative features of the 6000 series, these pedals provide vastly superior operation over the standard plastic OEM components.
Or you could just go super cheap and wrap a bungee cord around the brake or chuck a squash ball under it, but, you know...
Make your choice.