I don't know if you are interested, but they do sell an aftermarket rearveiw mirror that has the cumpass and temp. as well as the auto dimming feature, and looks just like the one GM puts in there trucks.
http://www.sportsimportsltd.com/hocoteaudilc.html
You can look here for examples. I think with the mirror you just have to run some wires to power it.
My grandparents have an Astro with the OH it has compass temp and MPG but it is also much bigger than the one in my truck, which has the sunglasses holder and map lights.