There is some interesting news on this front. One of the product lines I carry is Autosport Labs -- they have just introduced a new product that will accept 500Kbaud CAN ODB-II queries, and translate those older ODB-II protocols, as used on 1996-2007 vehicles without CAN-based ODB-II.
https://www.autosportlabs.com/new-produ ... c-adapter/
This may work for you. The Adapter is $99 in the US. Plus we would probably re-terminate it so work with the C125 standards loom.
Nick, where are you located? If you are interested in purchasing a C125 with this solution, I would be willing to do some testing to confirm it can work with the '02 WRX. If you're not located in the US, perhaps your local dealer would do the same.