Jeff, after a cursory search, far as I can tell so far, the options for including temp with compass will require losing the map lights / courtesy lights function, and may also require having nonfunctional OnStar buttons on the mirror.
There is an option that has map lights, and a display for compass/temp below the mirror, like this one:
It's a bit pricey, but it may be the only way to get all the functionality.
Mirrors with comp/temp are easy to find, if you don't care about the map lights. I could modify one of those for you (change display color+add ambient LED) if you wanted.