which car

 

if its the 04, i heard you may need the jdm bumper beam in order for you to mount the fog lights. or you have to cut into your US bumper beam.

http://www.gruppe-s.com/Subaru/subext.htm

if you scroll down to the lighting section, they mention it there.
though, they dont tell you how to do it.

 

i think outferno installed some fog lights on his STi. you might want to send him a PM to see if he has them on there and how they worked out.

 

if you get the jdm ones yes or u need to cut it i bought the jdm bumper beam, pm if you wanna know exactly what i did