Im going to have to do this too, VERY nice find to the original thread starter. I never would have thought of this unless i had actually been looking to do it and knew radio shack would have what i needed.
All I need is a little more info on where and how you routed the exterior temp sensor if you dont mind, maybe a few pics of a little better description. Thats the only part i forsee as a problem for me. Ive never been very good with "firewall" inclusive projects. (edit: figure it out, but had to jack teh car up to work underneath)
Oh and to anyone else that wants to do this, i suggest you hit your local radio shack soon, they only had 2 left at the store i went to, paid 9.99 but the sign there said 14.99 still, so im assuming its been discontinued for a new model or something to come in the near future. Unless im wrong and its just not a very popular item yet since nasioc hasnt found out about it until now.
EDIT: Just completed this mod, took just under 3 hours with taking my time dremeling the trim since i dont have an extra one. Heres some pics of the final product in my SRR 04 WRX Sedan. Enjoy!