This valve-less late model nipple found on STI models can be used to install an IAG AOS on the 2002-2003 WRX.

Does IAG have an Air Oil Separator that fits the 2002-2005 WRX?

 Answer: 
IAG does not make an AOS specifically for the 2.0L vehicles. You can purchase one for a 2006-07 WRX and relocate your cruise control. Additionally, the 2002-2003 WRX features a PCV nipple on the throttle body that also houses the PCV valve. This differs from 2004-07 STI’s, as they simply use a valve-less nipple at the same location.

If you are attempting the AOS install on a 2002-2003 WRX you will need to swap your PCV Nipple for the 2004-07 STI valve-less nipple PN# 14076AA030 found here.

Cruise Control Relocation:
Instructions to relocate the cruise control can be found here:

Instructions Link